THIS ANNOUNCEMENT IS NEITHER AN OFFER TO PURCHASE NOR A SOLICITATION OF AN
OFFER TO SELL SHARES. THE OFFER IS BEING MADE SOLELY BY THE OFFER TO PURCHASE
DATED MARCH 13, 2000 AND THE RELATED LETTER OF TRANSMITTAL AND IS BEING MADE TO
ALL HOLDERS OF SHARES. THE OFFER IS NOT BEING MADE TO (NOR WILL TENDERS BE
ACCEPTED FROM OR ON BEHALF OF) HOLDERS OF SHARES IN ANY JURISDICTION IN WHICH
THE MAKING OF THE OFFER OR THE ACCEPTANCE THEREOF WOULD NOT BE IN COMPLIANCE
WITH THE LAWS OF SUCH JURISDICTION. IN ANY JURISDICTION WHERE THE SECURITIES,
BLUE SKY OR OTHER LAWS REQUIRE THE OFFER TO BE MADE BY A LICENSED BROKER OR
DEALER, THE OFFER SHALL BE DEEMED TO BE MADE ON BEHALF OF THE PURCHASER BY J.P.
MORGAN SECURITIES INC., THE BEACON GROUP CAPITAL SERVICES, LLC OR ONE OR MORE
REGISTERED BROKERS OR DEALERS LICENSED UNDER THE LAWS OF SUCH JURISDICTION.

                      NOTICE OF OFFER TO PURCHASE FOR CASH
                     ALL OUTSTANDING SHARES OF COMMON STOCK
                                       OF
                               ONIX SYSTEMS INC.
                                       AT
                              $9.00 NET PER SHARE
                                       BY
                             ONIX ACQUISITION INC.
                          A WHOLLY-OWNED SUBSIDIARY OF
                         THERMO INSTRUMENT SYSTEMS INC.

    ONIX Acquisition Inc., a Delaware corporation (the "Purchaser") and a
wholly-owned subsidiary of Thermo Instrument Systems Inc., a Delaware
corporation ("Thermo Instrument"), is offering to purchase all outstanding
shares of common stock, par value $0.01 per share (the "Shares"), of ONIX
Systems Inc., a Delaware corporation (the "Company"), at a purchase price of
$9.00 per Share, net to the seller in cash, without interest thereon, upon
the terms and subject to the conditions set forth in the Offer to Purchase
dated March 13, 2000 (the "Offer to Purchase") and in the related Letter of
Transmittal (which, together with any amendments or supplements thereto,
collectively constitute the "Offer"). Thermo Electron Corporation, a Delaware
corporation ("Thermo Electron"), owns a majority of the outstanding shares of
common stock of Thermo Instrument.

         THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT,
   NEW YORK CITY TIME, ON FRIDAY APRIL 7, 2000, UNLESS THE OFFER IS EXTENDED.

    THE OFFER IS CONDITIONED UPON, AMONG OTHER THINGS, THERE BEING VALIDLY
TENDERED AND NOT WITHDRAWN PRIOR TO THE EXPIRATION OF THE OFFER THAT NUMBER
OF SHARES WHICH, TOGETHER WITH SHARES OWNED BY THERMO ELECTRON AND ITS
SUBSIDIARIES, INCLUDING THERMO INSTRUMENT, CONSTITUTES AT LEAST NINETY
PERCENT (90%) OF THE OUTSTANDING SHARES OF THE COMPANY ON THE EXPIRATION
DATE. THE OFFER IS ALSO SUBJECT TO CERTAIN OTHER IMPORTANT TERMS AND
CONDITIONS CONTAINED IN THE OFFER TO PURCHASE.

    The Offer is the first step in Thermo Instrument's plan to take the Company
private. The purpose of the Offer is to acquire the minority interest in the
Company as part of an overall reorganization of Thermo Electron. If the Offer is
completed, Thermo Electron, Thermo Instrument and the Purchaser together will
own at least 90% of the Shares. Promptly following the closing of the Offer,
Thermo Instrument and Thermo Electron plan to contribute their Shares to the
Purchaser and cause the Purchaser to merge with and into the Company in a
so-called "short-form" merger between the Company and the Purchaser (the




"Merger"). Stockholders of the Company who do not tender their Shares in the
Offer will not be entitled to vote on the Merger. The consideration per Share
in the Merger (other than with respect to Shares held by stockholders, if
any, who are entitled to and perfect their appraisal rights under Delaware
Law) would be the same as the Offer price of $9.00.

    For purposes of the Offer, the Purchaser will be deemed to have accepted for
payment, and thereby purchased, Shares validly tendered and not properly
withdrawn if, as and when the Purchaser gives oral or written notice to American
Stock Transfer & Trust Company (the "Depositary") of the Purchaser's acceptance
for payment of such Shares pursuant to the Offer. Upon the terms and subject to
the conditions of the Offer, payment for Shares so accepted for payment pursuant
to the Offer will be made by deposit of the aggregate purchase price therefor
with the Depositary, which will act as agent for tendering stockholders for the
purpose of receiving payment from the Purchaser and transmitting such payment to
stockholders whose Shares have been accepted for payment. UNDER NO CIRCUMSTANCES
WILL INTEREST ON THE PURCHASE PRICE FOR SHARES BE PAID, REGARDLESS OF ANY
EXTENSION OF THE OFFER OR ANY DELAY IN MAKING SUCH PAYMENT. In all cases,
payment for Shares tendered and accepted for payment pursuant to the Offer will
be made only after timely receipt by the Depositary of (i) certificates
evidencing Shares ("Share Certificates") or timely confirmation of a book-entry
transfer of such Shares into the Depositary's account at the Book-Entry Transfer
Facility (as defined in the section of the Offer to Purchase captioned "The
Tender Offer--Acceptance For Payment And Payment For Shares") pursuant to the
procedures set forth in the section of the Offer to Purchase captioned "The
Tender Offer--Acceptance For Payment And Payment For Shares," (ii) the Letter of
Transmittal (or a facsimile thereof), properly completed and duly executed, with
any required signature guarantees, or an Agent's Message (as defined in the
section of the Offer to Purchase captioned "The Tender Offer--Acceptance For
Payment And Payment For Shares") in connection with a book-entry transfer and
(iii) any other documents required by the Letter of Transmittal.

    The term "Expiration Date" means 12:00 midnight, New York City time, on
Friday, April 7, 2000, unless and until the Purchaser, in its sole discretion,
shall have extended the period during which the Offer is open, in which event
the term "Expiration Date" shall mean the latest time and date at which the
Offer, as so extended by the Purchaser, shall expire.

    Subject to the applicable rules and regulations of the Securities and
Exchange Commission, the Purchaser expressly reserves the right, in its sole
discretion, at any time and from time to time, to extend the period during
which the Offer is open for any reason, including the failure to satisfy any
of the conditions specified in the section of the Offer to Purchase captioned
"The Tender Offer-Certain Conditions Of The Offer," and thereby delay
acceptance for payment of, or payment for, any Shares, by giving oral or
written notice of such extension to the Depositary. Any such extension will
be followed as promptly as practicable by a public announcement thereof, such
announcement to be made no later than 9:00 a.m., New York City time, on the
next business day after the previously scheduled Expiration Date. During any
such extension, all Shares previously tendered and not properly withdrawn
will remain subject to the Offer, subject to the rights of a tendering
stockholder to withdraw such stockholder's Shares.

    Except as otherwise provided in the section of the Offer to Purchase
captioned "The Tender Offer--Withdrawal Rights," tenders of Shares made pursuant
to the Offer are irrevocable. Shares tendered pursuant to the Offer may be
withdrawn at any time prior to the Expiration Date and, unless theretofore
accepted for payment by the Purchaser pursuant to the Offer, may also be
withdrawn at any time after May 11, 2000. In order for a withdrawal to be
effective, a written, telegraphic or facsimile transmission notice of withdrawal
must be timely received by the Depositary at one of its addresses set forth on
the back cover of the Offer to Purchase. Any such notice of withdrawal must
specify the name of the person who tendered the Shares to be withdrawn, the
number of Shares to be withdrawn and the name of the registered holder of the
Shares to be withdrawn, if different from that of the person who tendered such
Shares. If Share Certificates to be withdrawn have been delivered or otherwise
identified to the Depositary, then, prior to the physical release of such Share
Certificates, the tendering stockholder must also submit the serial numbers
shown on such Share Certificates to the Depositary and the signatures on the

                                       2

notice of withdrawal must be guaranteed by an Eligible Institution (as defined
in the section of the Offer to Purchase captioned "The Tender Offer--Procedures
For Accepting The Offer And Tendering Shares"), unless such Shares have been
tendered for the account of an Eligible Institution. If Shares have been
tendered pursuant to the procedures for book-entry transfer, as set forth in the
section of the Offer to Purchase captioned "The Tender Offer--Procedures For
Accepting The Offer And Tendering Shares," any notice of withdrawal must specify
the name and number of the account at the Book-Entry Transfer Facility to be
credited with the withdrawn Shares and must otherwise comply with the procedures
of the Book-Entry Transfer Facility. Withdrawals may not be revoked and any
Shares properly withdrawn will thereafter be deemed not to have been validly
tendered for purposes of the Offer. However, withdrawn Shares may be retendered
at any time prior to the Expiration Date by following one of the procedures
described in the section of the Offer to Purchase captioned "The Tender
Offer--Procedures For Accepting The Offer And Tendering Shares." All questions
as to the form and validity (including the time of receipt) of any notice of
withdrawal will be determined by the Purchaser, in its sole discretion, whose
determination will be final and binding.

    The information required to be disclosed by Rule 14d-6(d)(1) and
13e-3(e)(1) of the General Rules and Regulations under the Securities
Exchange Act of 1934, as amended, is contained in the Offer to Purchase and
is incorporated herein by reference.

    The Company has provided the Purchaser with the Company's stockholders list
and security position listings for the purpose of disseminating the Offer to
holders of Shares. The Offer to Purchase and the related Letter of Transmittal
and, if required, other relevant material will be mailed to record holders of
Shares whose names appear on the Company's stockholders list and will be
furnished to brokers, dealers, commercial banks, trust companies and similar
persons whose names, or the names of whose nominees, appear on the Company's
stockholders list or, if applicable, who are listed as participants in a
clearing agency's security position listing for subsequent transmittal to
beneficial owners of Shares.

    The receipt of cash for Shares pursuant to the Offer will be a taxable
transaction for U.S. federal income tax purposes.

    THE OFFER TO PURCHASE AND THE RELATED LETTER OF TRANSMITTAL CONTAIN
IMPORTANT INFORMATION THAT SHOULD BE READ CAREFULLY BEFORE ANY DECISION IS MADE
WITH RESPECT TO THE OFFER.

    Tendering stockholders of record who tender shares directly will not be
obligated to pay brokerage fees or commissions or, except as set forth in
Instruction 6 of the Letter of Transmittal, stock transfer taxes on the purchase
of Shares by the Purchaser pursuant to the Offer. Stockholders who hold their
Shares through a bank or a broker should check with such institution as to
whether it charges any service fees. The Purchaser will pay the expenses of the
Depositary, D.F. King & Co., Inc., who is acting as the information agent (the
"Information Agent"), and J.P. Morgan Securities Inc. and The Beacon Group
Capital Services, LLC, who are acting as dealer managers (collectively, the
"Dealer Managers") in connection with the Offer.

    Questions and requests for assistance or for additional copies of the Offer
to Purchase, the Letter of Transmittal and all other tender offer materials may
be directed to the Information Agent or the Dealer Managers as set forth below,
and copies will be furnished promptly at the Purchaser's expense. No fees or
commissions will be paid to brokers, dealers or any other persons (other than
the Dealer Managers and the Information Agent) for soliciting tenders of Shares
pursuant to the Offer.

                                       3


                    THE INFORMATION AGENT FOR THE OFFER IS:

                             D.F. KING & CO., INC.
                          77 Water Street, 20th Floor
                               New York, NY 10005
                Bankers and Brokers call collect: (212) 269-5550
                   All Others Call Toll Free: (800) 290-6433

                     THE DEALER MANAGERS FOR THE OFFER ARE:

                          J.P. MORGAN SECURITIES INC.
                                 60 Wall Street
                               New York, NY 10260
                                 (877) 869-0656

                     THE BEACON GROUP CAPITAL SERVICES, LLC
                                399 Park Avenue
                               New York, NY 10022
                                 (212) 339-9100

March 13, 2000