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                           NOTICE OF SPECIAL MEETING

                                                                          , 1999

TO THE HOLDERS OF THE COMMON STOCK OF
THERMOSPECTRA CORPORATION

    I am pleased to give you notice of and cordially invite you to attend in
person or by proxy the Special Meeting of the stockholders of ThermoSpectra
Corporation, a Delaware corporation (the "Company" or "ThermoSpectra"), which
will be held on       ,   , 1999, at 10:00 a.m., at the offices of Thermo
Electron Corporation, 81 Wyman Street, Waltham, Massachusetts 02454, and at any
adjournment or adjournments thereof (the "Special Meeting"). At the Special
Meeting, stockholders will:

    1.  Consider and vote on a proposal to approve an Agreement and Plan of
       Merger dated as of May 21, 1999 (the "Merger Agreement") pursuant to
       which TS Acquisition Corporation, a newly-formed company (the "Merger
       Sub"), will be merged with and into ThermoSpectra (the "Merger"). Upon
       the Merger, each stockholder of the Company (other than stockholders who
       perfect their dissenters' rights, Thermo Instrument Systems Inc. ("Thermo
       Instrument") and Thermo Electron Corporation) will become entitled to
       receive $16.00 in cash, without interest, for each outstanding share of
       common stock, $.01 par value, of the Company (the "Common Stock") owned
       by such stockholder immediately prior to the effective time of the
       Merger. A copy of the Merger Agreement is attached as Appendix A to and
       is described in the accompanying Proxy Statement.

    2.  Transact such other business as may properly come before the Special
       Meeting.

    Only stockholders of record at the close of business on             , 1999
will receive notice of and be able to vote at the Special Meeting.

    The accompanying Proxy Statement describes the Merger Agreement, the
proposed Merger and the actions to be taken in connection with the Merger. The
Company's Bylaws require that the holders of a majority of the outstanding
shares of Common Stock entitled to vote be present or represented by proxy at
the Special Meeting in order to constitute a quorum for the transaction of
business. It is important that your shares be represented at the Special Meeting
regardless of the number of shares you hold. Whether or not you are able to be
present in person, please sign and return promptly the enclosed Proxy Card in
the accompanying envelope, which requires no postage if mailed in the United
States. You may revoke your proxy in the manner described in the accompanying
Proxy Statement at any time before it is voted at the Special Meeting.

    Stockholders who properly demand appraisal prior to the stockholder vote at
the Special Meeting, who do not vote in favor of adoption of the Merger
Agreement and who otherwise comply with the provisions of Section 262 of the
General Corporation Law of the State of Delaware (the "DGCL") will be entitled,
if the Merger is completed, to statutory appraisal of the fair value of their
shares of Common Stock. See "RIGHTS OF DISSENTING STOCKHOLDERS" in the
accompanying Proxy Statement and the full text of Section 262 of the DGCL, which
is attached as Appendix C to and is described in the accompanying Proxy
Statement, for a description of the procedures that you must follow in order to
exercise your appraisal rights.

    This Notice, the Proxy Card and Proxy Statement enclosed herewith are sent
to you by order of the Board of Directors.

                                          SANDRA L. LAMBERT
                                          SECRETARY

    WHETHER OR NOT YOU PLAN TO ATTEND, IT IS IMPORTANT THAT YOUR SHARES ARE
REPRESENTED AT THE SPECIAL MEETING. TO APPROVE AND ADOPT THE MERGER AGREEMENT,
THE AFFIRMATIVE VOTE OF A MAJORITY OF THE OUTSTANDING SHARES OF COMMON STOCK
ENTITLED TO VOTE THEREON IS REQUIRED. YOU ARE REQUESTED TO PROMPTLY COMPLETE,
SIGN AND DATE THE ENCLOSED PROXY CARD AND RETURN IT IN THE ENVELOPE PROVIDED.
YOU MAY REVOKE YOUR PROXY AT ANY TIME PRIOR TO ITS EXERCISE IN THE MANNER
DESCRIBED IN THE ATTACHED PROXY STATEMENT. ANY STOCKHOLDER PRESENT AT THE
SPECIAL MEETING MAY REVOKE SUCH HOLDER'S PROXY AND VOTE PERSONALLY ON THE MERGER
AGREEMENT AT THE SPECIAL MEETING.

    THE BOARD OF DIRECTORS RECOMMENDS THAT STOCKHOLDERS VOTE "FOR" APPROVAL AND
ADOPTION OF THE MERGER AGREEMENT. IN CONSIDERING THE RECOMMENDATION OF THE BOARD
OF DIRECTORS WITH RESPECT TO THE MERGER, STOCKHOLDERS OTHER THAN THERMO
INSTRUMENT, THERMO ELECTRON CORPORATION AND THE DIRECTORS AND OFFICERS OF THE
COMPANY, THERMO INSTRUMENT AND THERMO ELECTRON CORPORATION (THE "MINORITY
STOCKHOLDERS"), SHOULD BE AWARE THAT CERTAIN OFFICERS AND DIRECTORS OF THE
COMPANY HAVE CERTAIN INTERESTS THAT ARE IN ADDITION TO, OR DIFFERENT FROM, THE
INTERESTS OF THE MINORITY STOCKHOLDERS. SEE "SPECIAL FACTORS-- CONFLICTS OF
INTEREST."

    IF A PROPERLY EXECUTED PROXY CARD IS SUBMITTED AND NO INSTRUCTIONS ARE
GIVEN, THE SHARES OF COMMON STOCK REPRESENTED BY THAT PROXY WILL BE VOTED "FOR"
APPROVAL OF THE MERGER AGREEMENT.

    PLEASE DO NOT SEND YOUR STOCK CERTIFICATES TO THE COMPANY AT THIS TIME.