STOCK PURCHASE AGREEMENT

             This AGREEMENT is dated as of November 4, 1996 by and among
        Thermo Instrument Systems Inc., a Delaware corporation
        ("Seller"), and Thermo Optek Corporation, a Delaware corporation
        ("Buyer").

             WHEREAS, Seller desires to sell, or to cause its
        subsidiaries to sell, all of the shares of capital stock of ARL
        Applied Research Laboratories S.A. ("ARL") owned by the Seller
        (the "Shares") and the Buyer wishes to buy the Shares;

             NOW, THEREFORE, in consideration of the premises and mutual
        promises and agreements set forth herein, the parties hereto
        hereby agree as follows:

             1.  Purchase and Sale of Shares.    The Seller hereby sells,
        assigns, transfers, conveys, and delivers all of the Seller's
        right, title and interest in and to the Shares to the Buyer.  In
        consideration for the Shares, the Buyer shall pay to the Seller
        the sum of  $34,004,000  in cash (the "Purchase Price").  The
        Buyer and Seller acknowledge and agree that such Purchase Price
        represents the sum of (i) the net tangible assets of ARL (assumed
        to be $12,486,000) as of the date of the Seller's acquisition of
        the Shares as part of the acquisition on March 29, 1996 by the
        Seller and its subsidiaries of certain businesses of Fisons plc
        (the "Fisons Businesses") pursuant to the Amended and Restated
        Asset and Stock Purchase Agreement dated as of March 29, 1996
        among the Seller, Thermo Electron Corporation and Fisons plc (the
        "Restated Agreement"), plus (ii) a percentage of the total
        goodwill associated with the Seller's acquisition of the Fisons
        Businesses equal to the sales of ARL for the 1994 and 1995 fiscal
        years relative to the total sales of the Fisons Businesses for
        such years (the "ARL Percentage"), plus (iii) the ARL Percentage
        of the total costs incurred by the Seller in acquiring the Fisons
        Businesses and in restructuring the sales and service
        organization of the Fisons Businesses (the "Restructuring
        Costs").  The parties acknowledge that the purchase price paid by
        the Seller for the Fisons Businesses is subject to a post-closing
        adjustment based on the difference between the value of the net
        tangible assets of the Fisons Businesses as shown on the closing
        balance sheet dated as of March 29, 1996 (the "Closing Balance
        Sheet") and the target net tangible asset value provided for in
        the Restated Agreement.  In the event of any such adjustment, the
        Purchase Price shall be recalculated in accordance with the third
        sentence of this paragraph to account for (A) any adjustment in
        the net tangible assets (other than cash) of ARL as shown on the
        Closing Balance Sheet from $12,486,000), and (B) any adjustment
        in the total goodwill associated with Thermo's acquisition of the
        Fisons Businesses.  In addition, the purchase price shall be
        subject to recalculation in accordance with the third sentence of
        this paragraph in the event that the Restructuring Costs incurred
        are less than $2,453,000.  If any recalculation made pursuant to
        this paragraph results in an increase in the Purchase Price, the
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        Buyer shall pay the amount of such increase to the Seller, and if
        any such recalculation results in a decrease in the Purchase
        Price, the Seller shall pay the amount of such decrease to the
        Buyer.  Any payment made pursuant to the preceding sentence shall
        be made within ten days after the Closing Balance Sheet has
        become final (in the case of an adjustment related to the Closing
        Balance Sheet) and no later than March 29, 1997 (in the case of
        an adjustment related to the Restructuring Costs) and shall also
        be accompanied by interest from the date hereof calculated as
        provided in Section 4.1 of the Restated Agreement.

             2.   Further Assurances.  At the request of the Buyer at any
        time on or after the date hereof, the Seller will execute and
        deliver such further instruments of transfer and conveyance and
        take such other action as the Buyer reasonably may request
        effectively to assign and transfer to the Buyer the Shares.  

             3.   The Seller's Representations and Warranties.  The
        Seller represents and warrants that:

                  (a)  Organization and Standing.  The Seller is a
        corporation duly organized, validly     existing and in good
        standing under the laws of the State of Delaware.

                  (b)  Approval of Transactions.  The Seller has obtained
             all necessary corporate authorizations and approvals, and
             has taken all actions required for the execution and
             delivery of this Agreement and the consummation of the
             transactions contemplated hereby.

                  (c)  No Conflict.  Neither the execution nor delivery
             of this Agreement, nor the consummation of the transactions
             herein contemplated, nor the fulfillment of or compliance
             with the terms and provisions hereof will (1) conflict with
             the Certificate of Incorporation or By-laws of the Seller or
             the organizational documents of ARL, (2) violate any current
             provisions of law, administrative regulation, or court
             decree applicable to the Seller or ARL, (3) require the
             consent or approval of any governmental authority except for
             Swiss Lex Friederich approval, or (4) conflict with or
             result in a breach of any of the terms, conditions or
             provisions of or constitute default under any material
             agreement or instrument to which the Seller or ARL is a
             party or by which either is bound.

                  (d)  Capitalization of ARL.   The Shares constitute all
             of the issued and outstanding share capital of ARL.  The
             Shares have been duly authorized, validly issued and are
             fully paid and non-assessable.  The Seller holds good and
             marketable title to the Shares and will transfer the Shares
             to the Buyer pursuant to this Agreement free and clear of
             any liens, claims or encumbrances whatsoever.  No share
             capital of ARL is reserved for issuance, and there are no
             options, warrants, convertible securities or other rights,

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             agreements or commitments obligating ARL to issue any share
             capital.

             4.   The Buyer's Representations and Warranties.

                  (a)  Organization and Standing.  The Buyer is a
             corporation duly organized, validly existing and in good
             standing under the laws of the State of Delaware.

                  (b)  Approval of Transactions.  The Buyer has obtained
             all necessary corporate authorizations and approvals, and
             has taken all actions required for the execution and
             delivery of this Agreement and the consummation of the
             transactions contemplated hereby.

                  (c)  No Conflict.  Neither the execution nor delivery
        of this Agreement, nor the         consummation of the
        transactions herein contemplated, nor the fulfillment of or 
                  compliance with the terms and provisions hereof will
        (1) conflict with the                   Certificate of
        Incorporation or By-laws of the Buyer, (2) violate any current
        provisions          of law, administrative regulation, or court
        decree applicable to the Buyer, (3) require the              
        consent or approval of any governmental authority or (4) conflict
        with or result in a breach    of any of the terms, conditions or
        provisions of or constitute default under any material 
        agreement or instrument to which the Buyer is a party or by which
        it is bound.

             5.   Indemnification.

                  (a)  The Seller agrees to indemnify and hold harmless
        the Buyer from any and all damages, losses, liabilities, costs
        and expenses (including, without limitation, settlement costs and
        any reasonable legal, accounting or other expenses for
        investigating or defending any actions or threatened actions)
        incurred by the Buyer as a result of (i) any liability,
        commitment or obligation of ARL or any of its subsidiaries that
        result from any third party claim based upon the acts or
        omissions of ARL or such subsidiaries on or after March 29, 1996
        and prior to the effective date hereof,  (ii) the inaccuracy of
        any representation or warranty contained in Section 3 hereof or
        (iii) the breach by the Seller of any provision hereof.

                  (b)  The Buyer agrees to indemnify and hold harmless
        the Seller from any and all damages, losses, liabilities, costs
        and expenses (including, without limitation, settlement costs and
        any reasonable legal, accounting or other expenses for
        investigating or defending any actions or threatened actions)
        incurred by the Seller as a result of (i) the inaccuracy of any
        representation or warranty contained in Section 4 hereof, or (ii)
        the breach by the Buyer of any provision hereof.

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                  (c)  Whenever any claim shall arise for indemnification
        hereunder, the party seeking indemnification (the "Indemnified
        Party") shall promptly notify the other party (the "Indemnifying
        Party") of the claim and, when known, the facts constituting the
        basis for such claim.  In the event of any such claim for
        indemnification hereunder resulting from or in connection with
        any claim or legal proceedings by a third party, the notice to
        the Indemnifying Party shall specify, if known, the amount or an
        estimate of the amount of the liability arising therefrom.  The
        Indemnified Party shall not settle or compromise any claim by a
        third party for which the Indemnified Party is entitled to
        indemnification hereunder without the prior consent of the
        Indemnifying Party, unless suit shall have been instituted
        against the Indemnified Party and the Indemnifying Party shall
        not have taken control of such suit after notification thereof as
        provided in Section 5(d) of this Agreement.

                  (d)  In connection with any claim giving rise to
        indemnity hereunder resulting from or arising out of any claim or
        legal proceeding by a person who is not a party to this
        Agreement, the Indemnifying Party at its sole cost and expense
        may, upon notice to the Indemnified Party, assume the defense of
        any such claim or legal proceeding if it acknowledges to the
        Indemnified Party its obligations to indemnify the Indemnified
        Party with respect to all elements of such claim.  The
        Indemnified Party shall be entitled to participate in (but not
        control) the defense of any such action, with its counsel and at
        its own expense.  If the Indemnifying Party does not assume the
        defense of any such claim or litigation resulting therefrom
        within 30 days after the date the Indemnifying Party is notified
        of such claim pursuant to Paragraph 5(c) hereof, (i) the
        Indemnified Party may defend against such claim or litigation,
        after giving notice of the same to the Indemnifying Party, on
        such terms as are appropriate in the Indemnified Party's
        reasonable judgment, and (ii) the Indemnifying Party shall be
        entitled to participate in (but not control) the defense of such
        action, with its counsel and at its own expense.

             6.   Restated Agreement.  The Seller hereby assigns to the
        Buyer, and the Buyer hereby accepts and asssumes,  the Seller's
        rights and obligations under the Restated Agreement, and any
        agreements or instruments excuted by the Seller in connection
        therewith, but only to the extent such rights and obligations
        relate primarily ARL.  In furtherance of the foregoing, the Buyer
        may enforce, in its own name and in the name and on behalf of the
        Seller, any of the rights of the Seller under Section 11 of the
        Restated Agreement, and, if requested by the Buyer, the Seller
        shall take such actions, at its own expense, as the Buyer shall
        reasonably request in order that the Buyer shall have the full
        rights and benefits granted to it under this Section 6.
        .     
             7.   Transfer and Sales Tax.  Notwithstanding any provisions
        of law to the contrary, the Seller shall be responsible for and


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        shall pay all sales, transfer or stamp taxes, if any, upon the
        sale or transfer of the Shares hereunder.

             8.   Effective Date.  The transfer of the Shares shall be
        deemed to be effective as of the date hereof.

             9.   Captions.  The captions and headings to the various
        sections, paragraphs and exhibits of this Agreement are for
        convenience of reference only and shall not affect or control the
        meaning or interpretation of any of the provisions of this
        Agreement.

             10.  Integration.  This Agreement contains the entire
        understanding of the parties hereto with respect to the subject
        matter contained herein.

             11.  Notice of Communication.  Any notice or other
        communication shall be in writing and shall be personally
        delivered, or sent by overnight or second day courier or by first
        class mail, return receipt requested, to the party to whom such
        notice or other communication is to be given or made at such
        party's address set forth below, or to such other address as such
        party shall designate by written notice to the other party as
        follows:

             If to the Seller:

                  Thermo Instrument Systems Inc.
                  c/o Thermo Electron Corporation
                  81 Wyman Street
                  P.O. Box 9046
                  Waltham, MA  02445-9046
                  Attn: General Counsel

             If to the Buyer:

                  c/o Thermo Optek Corporation
                  81 Wyman Street
                  P.O. Box 9046
                  Waltham, MA  02445-9046
                  Attn: General Counsel

        provided that any notice of change of address, and any notice or
        other communication given otherwise than as specified above shall
        be effective only upon receipt; and further that any presumption
        of receipt by the addressee shall be inoperable during the period
        of any interruption in Postal Service.

             12.  Survival of Representations and Warranties.  All
        representations and warranties made by the Seller or the Buyer in
        this Agreement shall survive the execution and delivery of this
        Agreement.

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             13.  Governing Law; Assignment.  This Agreement is to be
        construed, interpreted, applied and governed in all respects in
        accordance with the laws of the Commonwealth of Massachusetts,
        without regard to its conflict of laws provisions, is to take
        effect as a sealed instrument, is binding upon and inures to the
        benefit of the parties hereto and their respect successors and
        assigns and may be canceled, modified or amended only by a
        written instrument executed by the Seller and the Buyer.  No
        party hereto may assign its rights hereunder without prior
        written consent of the other party.


























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                  IN WITNESS WHEREOF, the parties hereto have executed
        this Agreement as of the date and year first above written.


                                 THERMO OPTEK CORPORATION


                                 By:  Robert J. Rosenthal
                                     ------------------------------------
                                      Robert J. Rosenthal
                                      Senior Vice President


                                 THERMO INSTRUMENT SYSTEMS INC.



                                 By:  Earl R. Lewis
                                     ------------------------------------
                                      Earl R. Lewis
                                      Executive Vice President and Chief
                                       Operating Officer