EXHIBIT 4.4

                (FORM OF FACE OF REGISTERED GLOBAL SECURITIES)

Unless this Security is presented by an authorized representative of The
Depository Trust Company ("DTC"), 55 Water Street, New York, New York to the
issuer or its agent for registration of transfer, exchange or payment, and such
Security issued is registered in the name of CEDE & CO., or such other name as
requested by an authorized representative of DTC, ANY TRANSFER, PLEDGE OR OTHER
USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL, since the
registered owner hereof, CEDE & CO., has an interest herein.

Unless and until this Security is exchanged in whole or in part for Securities
in certificated form, this Security may not be transferred except as a whole by
DTC to a nominee thereof or by a nominee thereof to DTC or another nominee of
DTC or by DTC or any such nominee to a successor of DTC or a nominee of such
successor.

                        THERMO INSTRUMENT SYSTEMS INC.
                    (Incorporated in the State of Delaware)


                 4% CONVERTIBLE SUBORDINATED GLOBAL DEBENTURE
                             DUE JANUARY 15, 2005
                     GUARANTEED ON A SUBORDINATED BASIS BY
                          THERMO ELECTRON CORPORATION
                    (Incorporated in the State of Delaware)

No. R-________________

Cusip: 883559AE6
      ________________

     Thermo Instrument Systems Inc., a Delaware corporation (herein referred
to as the "Company," which term includes any successor corporation under the
Indenture referred to on the reverse hereof), for value received, hereby
promises to pay to Cede & Co. or registered assigns the principal sum of _______
Dollars (or any other amounts as are endorsed on the Schedule of Adjustments
hereto) plus any premium, if any, on January 15, 2005 (the "Stated Maturity")
upon the presentation and surrender hereof or, at the option of the Company, in
whole or in part at any time on or after January 15, 2001, upon notice as
described in the Indenture and to pay interest thereon from January 21, 1998 or
from the most recent Interest Payment Date to which interest has been paid or
duly provided for, semi-annually in arrears on January 15 and July 15 in each
year (each, an "Interest Payment Date"), commencing July 15, 1998, at the rate
of 4% per annum, and Additional Amounts, if any, until the principal hereof is
paid or duly provided for. The interest and Additional Amounts, if any, so
payable, and punctually paid or duly provided for, on any Interest Payment Date
will, as provided in such Indenture, be paid to the Holder in whose name this
Security (or one or more Predecessor Securities) is registered at the close of
business on the Regular Record Date for such interest, which shall be the
January 1 or July 1 (whether or not a Business Day), as the case may be, next
preceding such Interest

 
Payment Date at the Office or Agency of the Company maintained for such
purpose; provided, however, that such interest may be paid, at the Company's
         --------  -------
option, by mailing a check to such Holder at its registered address or by
transfer of funds to an account maintained by such Holder within the United
States. Any such interest not so punctually paid or duly provided for shall
forthwith cease to be payable to the Holder on such Regular Record Date, and may
be paid to the Holder in whose name this Security (or one or more Predecessor
Securities) is registered at the close of business on a Special Record Date for
the payment of such Defaulted Interest to be fixed by the Trustee, notice
whereof shall be given to Holders of Securities of this series not less than 10
days prior to such Special Record Date, or may be paid at any time in any other
lawful manner not inconsistent with the requirements of any securities exchange
on which the Securities of this series may be listed, and upon such notice as
may be required by such exchange, all as more fully provided in the Indenture.
Interest will be computed on the basis of a 360-day year of twelve 30-day
months. All payments hereunder shall be made in United States Dollars.

     Subject to the applicable provisions of the Indenture, the aggregate
principal amount represented by this global Security may be decreased to reflect
exchanges or partial conversions, redemptions or repayments, by endorsing the
Schedule of Adjustments hereto, and the principal amount hereof shall be deemed
to be decreased for all purposes by the amount so exchanged, converted, redeemed
or repaid, as applicable.

     Reference is hereby made to the further provisions of this Security set
forth on the reverse hereof, which further provisions shall for all purposes
have the same effect as if set forth at this place.

     Unless the Certificate of Authentication hereon has been executed by
the Trustee by manual signature of one of its authorized signatories, this
Security shall not be entitled to any benefit under the Indenture, or be valid
or obligatory for any purpose.

                                      -2-

 
     IN WITNESS WHEREOF, the Company has caused this instrument to be duly
executed under its facsimile corporate seal.

Dated:  January __, 1998                     THERMO INSTRUMENT SYSTEMS INC.

                                             By:_______________________
Attest:                                          [Name]
                                                 [Title]
_______________________________
Secretary

[SEAL]


                          CERTIFICATE OF AUTHENTICATION

         This is one of the Securities of the series designated therein referred
to in the within-mentioned Indenture.

                                                  BANKERS TRUST COMPANY,
                                                  as Trustee


                                                  By:________________________
                                                      Authorized Officer

                                      -3-

 
               (FORM OF REVERSE OF REGISTERED GLOBAL SECURITIES)

                        THERMO INSTRUMENT SYSTEMS INC.


     This Security is one of a duly authorized issue of securities of the
Company (herein called the "Securities"), issued and to be issued in one or more
series under an Indenture, dated as of January 15, 1998 (herein called the
"Indenture") by the Company, as issuer, and Thermo Electron Corporation, as
guarantor (herein called the "Guarantor," which term includes any successor
corporation under the Indenture), to Bankers Trust Company, as Trustee (herein
called the "Trustee," which term includes any successor trustee under the
Indenture with respect to the series of which this Security is a part), to which
Indenture and all indentures supplemental thereto reference is hereby made for a
statement of the respective rights, limitations of rights, duties and immunities
thereunder of the Company, the Guarantor, the Trustee and the Holders of the
Securities and any Coupons appertaining thereto, and of the terms upon which the
Securities are, and are to be, authenticated and delivered. This Security is one
of the duly authorized series of Securities designated on the face hereof and
the aggregate principal amount of the Securities to be issued under such series
is limited to $250,000,000 (except for Securities authenticated and delivered
upon transfer of, or in exchange for, or in lieu of other Securities). The
Guarantor has unconditionally guaranteed on a subordinated basis the payment of
principal, premium, if any, and interest on the Securities. The Holders of the
Securities will be entitled to the benefits of, be bound by, and be deemed to
have notice of, all of the provisions of the Indenture. A copy of the Indenture
is on file and may be inspected at the office of the Paying Agents appointed by
the Company. All terms used in this Security which are defined in the Indenture
shall have the meanings assigned to them in the Indenture.

     The Securities are issuable as bearer securities (the "Bearer
Securities"), with interest Coupons attached, in the denominations of U.S.
$1,000 and U.S. $10,000, and as registered securities (the "Registered
Securities"), without Coupons, in denominations of U.S. $1,000 and integral
multiples thereof, except as otherwise provided in or pursuant to the Indenture.
The Registered Securities, and transfers thereof, shall be registered as
provided in the Indenture. The holder of any Bearer Security or any Coupon
appertaining thereto and the registered holder of a Registered Security shall
(to the fullest extent permitted by applicable law) be treated at all times, by
all persons and for all purposes as the absolute owner of such Security or
Coupon, as the case may be, regardless of any notice of ownership, theft or loss
or of any writing thereon. Bearer Securities may be exchanged for Registered
Securities as set forth in the Indenture. Registered Securities may not be
exchanged for Bearer Securities.

     The Securities are general, unsecured obligations of the Company,
subordinated in right of payment to the prior payment in full of all existing
and future Senior Indebtedness of the Company to the extent set forth in Article
Seventeen of the Indenture. There are no restrictions herein on other
indebtedness or securities which may be incurred or issued by the Company or the
Guarantor.

     Additional Amounts shall be payable on the Securities as set forth in
the Indenture.

                                      -4-

 
     If an Event of Default, as defined in the Indenture, shall occur and be
continuing, the principal of the Securities of this series may be declared due
and payable in the manner and with the effect provided in the Indenture.

     Subject to the terms of the Indenture, the Securities are convertible
at any time prior to Maturity at an initial Conversion Price of $35.65 per
share, subject to adjustment as provided in the Indenture. Accrued interest from
the immediately preceding Interest Payment Date until the Conversion Date will
be paid within five Business Days after the Conversion Date. In case this
Security, or a portion thereof, is called for redemption, or is delivered for
repayment, the conversion right in respect of this Security or a portion thereof
so called and delivered shall expire on the close of business on the fifth
Business Day preceding the Redemption Date or the second Business Day preceding
a repayment on the Repayment Date, as the case may be, unless the Company
defaults in making the payment due upon redemption or repayment, as the case may
be. To convert this Security, the Holder must surrender this Security, duly
endorsed or assigned to the Company, at any applicable Place of Conversion,
accompanied by a duly signed conversion notice. Bearer Securities surrendered
for conversion must be surrendered together with all Coupons appertaining
thereto that mature after the Conversion Date, except as otherwise provided in
the Indenture.

     The Securities are subject to redemption at any time on or after
January 15, 2001, as a whole or in part, at the option of the Company, at a
Redemption Price equal to 100% of the principal amount, together in the case of
any such redemption with accrued interest to the Redemption Date as provided in
the Indenture. Notice of redemption will be given to Holders of Securities, not
less than 20 nor more than 60 days prior to the Redemption Date, all as provided
in the Indenture. Subject to the terms of the Indenture, if as a result of a Tax
Law Change the Company has or will become obligated to pay to the Holder of any
Tax Affected Security Additional Amounts, and such obligation cannot be avoided
by the Company taking reasonable measures available to it, then the Company may,
at its option, redeem the Tax Affected Securities as a whole, but not in part,
upon not less than 20 nor more than 60 days' notice to the Holders prior to the
Redemption Date therefor, at a Redemption Price equal to 100% of the principal
amount plus interest accrued to the Redemption Date, and any Additional Amounts
then payable.

     Subject to the terms of the Indenture, the Securities are subject to
repayment at the option of the Holder thereof, in whole or in part, on the
Repayment Date, if the Common Stock (or other equity securities into which this
Security is then convertible) is neither listed for trading on a United States
national securities exchange, the Nasdaq National Market nor approved for
trading on an established automated over-the-counter trading market in the
United States. In such event, the Securities shall be repaid at a price equal to
the principal amount hereof, plus accrued interest and Additional Amounts, if
any. The Holders of Securities of this series desiring to be repaid must deliver
(1) this Security with the "Option to Elect Repayment" duly signed and
completed, or (2) such other documentation as may be provided by the Indenture,
to the Trustee at the Place of Payment not earlier than 60 days nor later than
30 days prior to the Repayment Date. Bearer 

                                      -5-

 
Securities must be surrendered together with all Coupons appertaining thereto
that mature after the Repayment Date, except as otherwise provided in the
Indenture.

     The Place of Payment, place of registration of transfer and exchange
and the Place of Conversion for the Registered Securities and the Guarantees
endorsed thereon, shall be the Borough of Manhattan, The City of New York, and
the Corporate Trust Office of the Trustee shall be the Company's and the
Guarantor's Office or Agency in the Borough of Manhattan, The City of New York
for such purpose. The Places of Payment and Places of Conversion for the Bearer
Securities and the Guarantees endorsed thereon, shall be London, England and
Luxembourg, and the offices of the Trustee in London and Luxembourg shall be the
Offices or Agencies for such purpose and the offices of the Trustee in London
and Luxembourg shall be the Company's and the Guarantor's Paying Agent in London
and Luxembourg, respectively.

     The Trustee initially shall be the Security Registrar, one of the
Authenticating Agents, the Paying Agent and the Conversion Agent. The Trustee
presently has its Corporate Trust Office at Four Albany Street, 4th Floor, New
York, NY 10006, its Office in London at 1 Appold Street, Broadgate, London, EC2A
2HE, England, and its Office in Luxembourg at 14 Boulevard F.D. Roosevelt,
L-2450 Luxembourg. The Company and the Guarantor may subsequently appoint an
Office or Agency in addition to or other than the Borough of Manhattan, The City
of New York with respect to the Registered Securities and London, England and
Luxembourg with respect to the Bearer Securities.

     The Indenture permits, with certain exceptions as therein provided, the
amendment thereof and the modification of the rights and obligations of the
Company and the Guarantor and the rights of the Holders of the Securities under
the Indenture at any time by the Company, the Guarantor and the Trustee with the
consent of the Holders of not less than a majority of the aggregate principal
amount of all Securities issued under the Indenture at the time Outstanding and
affected thereby. The Indenture also contains provisions permitting the Holders
of not less than a majority of the aggregate principal amount of the Outstanding
Securities, on behalf of the Holders of all such Securities, to waive compliance
by the Company and the Guarantor with certain provisions of the Indenture.
Furthermore, provisions in the Indenture permit the Holders of not less than a
majority of the aggregate principal amount, in certain instances, of the
Outstanding Securities of any series to waive, on behalf of all of the Holders
of Securities of such series, certain past defaults under the Indenture and
their consequences. Any such consent or waiver by the Holder of this Security
shall be conclusive and binding upon such Holder and upon all future Holders of
this Security and other Securities issued upon the registration of transfer
hereof or in exchange herefor or in lieu hereof, whether or not notation of such
consent or waiver is made upon this Security.

     No reference herein to the Indenture and no provision of this Security
or of the Indenture shall alter or impair the obligation of the Company, which
is absolute and unconditional (except as to the specific subordination
provisions contained in Article Seventeen of the Indenture), to pay the
principal of, premium, if any, interest and Additional Amounts, if any, on this
Security at the times, places and rates, and in the coin or currency, herein
prescribed.

                                      -6-

 
     No service charge shall be made for any registration of transfer or
exchange, but the Company may require payment of a sum sufficient to cover any
tax or other governmental charge payable in connection therewith.

     The Indenture and the Securities shall be governed by and construed in
accordance with the laws of the Commonwealth of Massachusetts applicable to
agreements made and to be performed entirely in such Commonwealth except that
the rights, protections, obligations, indemnities and immunities of the Trustee
under the Indenture and the Securities shall be governed by the laws of the
State of New York, without regard to the principles of conflicts of laws of
either state.

                                      -7-

 
                            SCHEDULE OF ADJUSTMENTS

                                          Remaining           Notation
                Principal                 principal amount    made on
                amount                    following such      behalf of the
Date made       adjustment                adjustment          Trustee
                                                            
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- -------------------------------------------------------------------------------

                                      -8-

 
                                    GUARANTEE

     For value received, Thermo Electron Corporation, a corporation
organized under the laws of the State of Delaware (herein called the
"Guarantor," which term includes any successor corporation under the Indenture
referred to in the Security upon which this Guarantee is endorsed), hereby
unconditionally guarantees to the Holder of the Security upon which this
Guarantee is endorsed and to the Trustee on behalf of the Trustee and such
Holder the due and punctual payment of the principal of, premium, if any, and
interest and Additional Amounts, if any, on such Security, any other amount due
and payable pursuant to the terms of the Indenture and the due and punctual
payment of the sinking fund or analogous payments referred to therein if any,
when and as the same shall become due and payable, whether at the Stated
Maturity, by declaration of acceleration, call for redemption, repayment at the
option of the Holder or otherwise, according to the terms thereof and of the
Indenture. In case of the failure of Thermo Instrument Systems Inc., a
corporation organized under the laws of Delaware (herein called the "Company,"
which term includes any successor corporation under such Indenture), punctually
to make any such payment of principal, premium, if any, or interest or
Additional Amounts, if any, the Guarantor hereby agrees to cause any such
payment to be made punctually when and as the same shall become due and payable,
whether at the Stated Maturity or by declaration of acceleration, call for
redemption, repayment at the option of the Holder or otherwise, and as if such
payment were made by the Company.

     The Guarantor hereby agrees that its obligations hereunder shall be as
if it were principal debtor and not merely surety, and shall be absolute and
unconditional (except as to the specific subordination provisions contained in
Article Eighteen of the Indenture), irrespective of, and shall be unaffected by,
any invalidity, subordination, irregularity or unenforceability of such Security
or such Indenture, any failure to enforce the provisions of such Security or
such Indenture, or any waiver, modification or indulgence granted to the Company
with respect thereto, by the Holder of such Security or the Trustee or any other
circumstance which may otherwise constitute a legal or equitable discharge of a
surety or guarantor. The Guarantor hereby waives the benefits of diligence,
presentment, demand of payment, filing of claims with a court in the event of
merger, insolvency or bankruptcy of the Company, any right to require a
proceeding first against the Company, protest or notice with respect to such
Security or the indebtedness evidenced thereby and all demands whatsoever, and
covenants that this Guarantee will not be discharged except by strict and
complete performance of the obligations contained in such Security and this
Guarantee. The Guarantor hereby agrees that, in the event of a default in
payment of principal of, premium, if any, and interest, and Additional Amounts,
if any, on such Security, or default in any sinking fund or analogous payment
referred to therein, legal proceedings may be instituted by the Trustee on
behalf of, or by, the Holder of such Security, on the terms and conditions set
forth in the Indenture, directly against the Guarantor to enforce this Guarantee
without first proceeding against the Company.

     The Guarantor shall be subrogated to all rights of the Holder of such
Security and the Trustee against the Company in respect of any amounts paid to
such Holder by the Guarantor on account of such Security pursuant to the
provisions of this Guarantee or the Indenture; provided, however, that the
                                               --------  -------
Guarantor shall not be entitled to enforce, or to receive any payments arising

                                      -9-

 
out of or based upon, such right of subrogation until the principal of, premium,
if any, and interest and Additional Amounts, if any, on all Securities issued
under such Indenture shall have been paid in full.

     Claims under this Guarantee are, to the extent provided in the
Indenture, subject in right of payment to the prior payment in full of all
Senior Guarantor Indebtedness, and this Guarantee is issued subject to the
provisions of the Indenture with respect thereto. Each Holder of a Security upon
which this Guarantee is endorsed, by accepting the same, (a) agrees to and shall
be bound by such provisions, (b) authorizes and directs the Trustee on his
behalf to take such action as may be necessary or appropriate to effectuate the
subordination so provided and (c) appoints the Trustee his, her or its
attorney-in-fact for any and all such purposes.

     No reference herein to such Indenture and no provision of this
Guarantee or of such Indenture shall alter or impair the guarantee of the
Guarantor, which is absolute and unconditional (except as to the specific
subordination provisions contained in Article Eighteen of the Indenture), of the
due and punctual payment of principal, premium (if any), and interest and
Additional Amounts, if any, on the Security upon which this Guarantee is
endorsed.

     This Guarantee shall not be valid or obligatory for any purpose until
the certificate of authentication of the Security upon which this Guarantee is
endorsed shall have been manually executed by or on behalf of the Trustee under
such Indenture.

     All terms used in this Guarantee which are defined in such Indenture
shall have the meanings assigned to them in such Indenture.

     This Guarantee shall be deemed to be a contract made under the laws of
the Commonwealth of Massachusetts, and for all purposes shall be governed by and
construed in accordance with the laws of the Commonwealth of Massachusetts.

     IN WITNESS WHEREOF, the Guarantor has caused this Guarantee to be duly
executed under its corporate seal and dated the date on the face hereof.

                                             THERMO ELECTRON CORPORATION


Attest:______________________________        By: _____________________________

                                             Title: __________________________

                                      -10-

 
         This is one of the Securities of the series designated therein referred
to in the within-mentioned Indenture.

Dated:  _______________________              BANKERS TRUST COMPANY,
                                             as Trustee



                                             By: ______________________________
                                                       Authorized Officer

                                      -11-

 
                                 TRANSFER NOTICE


FOR VALUE RECEIVED, the undersigned Holder hereby sell(s), assign(s) and 
transfer(s) unto ______________________________________________________________
whose taxpayer identification number is _____________________ and whose address
including postal/zip code is _____________________________________ the within
Security and all rights thereunder, hereby irrevocably constituting and
appointing _____________________________ attorney-in-fact to transfer said
Security on the books of the Security Registrar with full power of substitution
in the premises.


Dated: __________________________      Name: ____________________________

                                       By: ______________________________

                                       Title: ___________________________

                                       NOTICE: The signature of the
                                       Holder to this assignment must
                                       correspond with the name as
                                       written upon the face of the
                                       within instrument in every
                                       particular, without enlargement
                                       or any change whatsoever.

                                       SIGNATURE GUARANTEED


                                       ____________________________________


                                      -12-

 
                               CONVERSION NOTICE



     The undersigned Holder of this Security hereby irrevocably exercises
the option to convert this Security, or any portion of the principal amount
hereof (which is an integral multiple of U.S. $1,000 below designated), into
shares of Common Stock in accordance with the terms of the Indenture referred to
in this Security, and directs that such shares, together with a check in payment
for any fractional share and any Securities representing any unconverted
principal amount hereof, be delivered to and be registered in the name of the
undersigned unless a different name has been indicated below. If shares or
Securities are to be registered in the name of a Person other than the
undersigned, the undersigned will pay all transfer taxes payable with respect
thereto.


Dated: ___________________________          ___________________________________
                                                          Signature
                                            [MUST BE GUARANTEED IF STOCK
                                            OR SECURITIES ARE TO BE ISSUED
                                            IN A NAME OTHER THAN THE 
                                            REGISTERED HOLDER OF THE
                                            SECURITY]

____________________________________
               Name

____________________________________
             Address

____________________________________
Social Security or other Taxpayer 
Identification Number, if any

                                      -13-

 
If shares or Registered Securities are     If only a portion of the Securities 
to be registered in the name of a Person   is to be converted, please indicate:
other than the Holder, please print
such Person's name and address:            1. Principal amount to be converted:

                                           U.S. $___________________

_______________________________            2. Principal amount and denomination
            Name                              of Registered Securities
                                              representing unconverted
                                              principal amount to be issued.
_______________________________
           Address
                                           Amount:  U.S.$_________________
_______________________________
Social Security or other Taxpayer          Denominations:
Identification Number, if any              U.S.$__________
                                           (any integral multiple of 
                                            U.S. $1,000)

_______________________________



                           OPTION TO ELECT REPAYMENT
                            UPON A REPAYMENT EVENT


To:  Thermo Instrument Systems Inc.

     The undersigned owner of this Security hereby acknowledges receipt of a
notice from Thermo Instrument Systems Inc.(the "Company") as to the occurrence
of a Repayment Event with respect to the Common Stock of the Company and
requests and instructs the Company to repay the entire principal amount of this
Security, or the portion thereof (which is $1,000 or an integral multiple
thereof) below designated, in accordance with the terms of the Indenture
referred to in this Security at the Repayment Price (or the relevant percentage
thereof), together with accrued interest to such date (except if the Repayment
Date shall be an Interest Payment Date), to the holder hereof.


Dated: ________________________


                                              _______________________________
                                              Signature*(s)

                                      -14-

 
                                              Name: ___________________________
                                              Address:_________________________

                                                 ______________________________
                                              [* Signature Guarantee Required]

                                              Principal amount to be repaid
                                              (if less than all):

                                              $__________________

                                              NOTICE: If this Security is
                                              issued in registered form, the
                                              above signatures of the
                                              holder(s) hereof must
                                              correspond with the name as it
                                              appears in the Security in
                                              every particular without
                                              alteration or enlargement or
                                              any change whatever.


_______________________________
Social Security or Other
Taxpayer Identification Number

                                      -15-