EXHIBIT 2.2


                                AGREEMENT AND RELEASE

                  This Agreement and Release, entered into as of the 15th
        day of December, 1997, by and between Fisons plc, an English
        company ("Fisons"), on the one hand, and Thermo Instrument
        Systems Inc., a Delaware corporation ("Thermo"), and Thermo
        Electron Corporation, a Delaware corporation ("Thermo Electron"),
        on the other hand (all of whom are sometimes referred to as
        "parties").

                                       RECITALS


        A.   The parties hereto have previously entered into an Amended
        and Restated Asset and Stock Purchase Agreement (the
        "Agreement"), dated as of March 29, 1996, pursuant to which
        Fisons sold a portion of its scientific instruments business to
        Thermo.

        B.   Pursuant to Section 4.1 of the Agreement, which provides for
        a possible post-closing adjustment to the purchase price, Fisons
        in 1996 delivered to Thermo a draft closing balance sheet with
        respect to the business sold.  Thereafter, Thermo asserted
        certain objections and other claims with respect to that draft
        closing balance sheet, which it claimed entitled it to a
        reduction in the purchase price, plus interest thereon.
        Subsequently, Thermo made certain other claims with respect to
        the resale to Fisons pursuant to Section 7.16 of the Agreement of
        certain accounts receivable.  All such objections and claims are
        referred to herein as the "Asserted Claims".

        C.   The parties desire to resolve the Asserted Claims amicably,
        without any admission of liability, on the terms and conditions
        set forth herein.

                                    AGREEMENT

             NOW, THEREFORE, Fisons, Thermo and Thermo Electron, in
        consideration of the foregoing and the mutual promises and
        obligations contained herein, and intending to be legally bound
        hereby, covenant and agree as follows:


                  1.   In consideration of the terms hereof, the releases
        granted hereby and the other covenants herein, Fisons shall pay
        to Thermo the sum of TWENTY-FOUR MILLION FOUR HUNDRED FIFTY-SIX
        THOUSAND SEVEN HUNDRED EIGHTY-THREE British Pounds Sterling
        (BPS24,456,783) (collectively, the "Settlement Funds"), as set
        forth below by wire transfer to the following bank and account
        number:
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             Barclays Bank Plc

             London England


             Sort Code 20-00-00

             For: Thermo Instrument Systems Inc.

             Account Number xxxxxxxx

             Attention: North American Team

             The Settlement Funds are compromised of the following
        constituent amounts:


                  (a)  2,475,000 British Pounds Sterling, in respect of
        Claims (as defined below) relating to the matters provided for in
        Section 7.16 of the Agreement;

                  (b)  19,650,000 British Pounds Sterling, in respect of
        all other Claims (as defined below) released hereunder;

                  (c)  2,331,783 British Pounds Sterling, representing
        interest on the amount provided for in subparagraph (b) above.

             Fisons shall pay the Settlement Funds in full on January 2,
        1998.  The effectiveness of this Agreement and Release is
        conditioned upon Thermo's receipt of the Settlement Funds.

             2.   2.1  In consideration of the delivery of the Settlement
        Funds as set forth above in paragraph 1, each of Thermo and
        Thermo Electron does, for and on behalf of itself as well as all
        persons claiming by, through or under it (including without
        limitation all past, present and future parents, predecessors,
        successors, subsidiaries, affiliates and assigns, their
        respective past, present and future directors, officers,
        employees, agents, attorneys and insurers, and administrators
        thereof) (individually and collectively, "Releasors"), hereby
        irrevocably and unconditionally acknowledges complete
        satisfaction of, and does hereby remise, release and forever
        discharge Fisons, its past, present and future parents,
        predecessors, successors, subsidiaries, affiliates and assigns,
        their respective past, present and future directors, officers,
        shareholders, employees, agents, attorneys and insurers, and
        administrators thereof (including without limitation
        Rhone-Poulenc Rorer Inc.) (individually and collectively,
        "Releasees") of and from, any and all claims, demands, causes of
        action, suits, debts, sums of money, accounts, covenants,
        contracts, controversies, agreements, promises, damages and

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        judgments ("Claims") of any kind or nature whatsoever, in law or
        in equity, known or unknown, existing or contingent, suspected or
        unsuspected, within this or any jurisdiction, that it ever had or
        may have had or may now or hereafter have, arising from or
        relating to:

                  (a)  any matter provided for in any one or more of the
                  following Sections of the Agreement:

                       (i)  Section 3.2(b) insofar as it relates to any
                       liability for a warranty obligation released under
                       paragraph 2.1(a)(iii) of this Agreement and
                       Release or any liability for a product liability
                       claim released under paragraph 2.1(a)(ii) of this
                       Agreement and Release (and, for the avoidance of
                       doubt, the release under this paragraph 2.1(a)(i)
                       of this Agreement and Release shall not affect any
                       Claim under such Section 3.2 (b) with respect to
                       the lawsuit Biacore, AB and Biacore, Inc. v.
                       Thermo Bioanalysis Corporation, U.S.D.C., D. Del,
                       No. 97-274);


                       (ii) Section 3.2(f) insofar as it relates to any
                       liability for a product liability claim asserted
                       on or prior to the date hereof with respect to an
                       occurrence after the Closing (as defined in the
                       Agreement);

                       (iii)     Section 3.2(j), except for any Claim
                       under Section 3.2(j) with respect to the lawsuit
                       The Purdue Frederick Company v. Fisons
                       Instruments, Inc., and VG Laboratory Systems
                       Limited, U.S.D.C., S.D.N.Y. No. 97 CV-0898;

                       (iv) Section 4.1;

                       (v)  Section 5, except for the representations and
                       warranties set forth therein that are identified
                       in Section 11.3(c)(i) of the Agreement as
                       surviving without time limit;

                       (vi) Section 7.16;


                       (vii)     Section 11.1(a) insofar as it relates to
                       representations and warranties with respect to
                       which Claims are released hereunder;

                       (viii)    Section 11.1(b) insofar as it relates to
                       covenants or agreements with respect to which
                       Claims are released hereunder;

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                       (ix) Section 11.1(c) insofar as it relates to
                       Excluded Liabilities (as defined in the Agreement)
                       with respect to which Claims are released
                       hereunder;

                       (x)  Section 11.1(d) insofar as it relates to
                       Excluded Company Liabilities (as defined in the
                       Agreement) corresponding to the Excluded
                       Liabilities with respect to which Claims are
                       released hereunder; and

                       (xi) all other Sections or portions thereof of the
                       Agreement, except for the Sections and matters set
                       forth below in paragraph 2.2 of this Agreement and
                       Release; provided, however, that each Claim (other
                       than an Asserted Claim or any Claim for a matter
                       that is known to any Releasor as of the date
                       hereof) arising from or relating to any matter
                       provided for in any such other Sections of the
                       Agreement shall be excluded from the release under
                       this paragraph 2.1(a)(xi) to the extent the Losses
                       (as defined in the Agreement) incurred or suffered
                       by Thermo as a result of such Claim exceed ONE
                       MILLION UNITED STATES DOLLARS (US $1,000,000); and
                       provided further that in determining whether such
                       threshold has been exceeded all Claims arising out
                       of separate occurrences shall be treated as
                       separate Claims except that Claims arising out of
                       the same or similar circumstances or the same text
                       of the Agreement shall be treated as a single
                       Claim; and/or


                  (b)  the Asserted Claims and/or the subject matter
        thereof.

                  2.2  The release under paragraph 2.1(a)(xi) of this
        Agreement and Release shall not extend to any one or more of the
        following Sections of the Agreement:

                  (a)  Sections 2.7; 2.8; 2.9; 3.2(a), (c), (d), (e),
                  (g), (h), (i), (k), (l), (m), and (n); 4.2; 4.3; 7.6;
                  7.7(a), (b) and (c); 7.8; 7.9; 7.10(b); 7.12; 7.13;
                  7.14; 7.15; 7.17; 7.19; 7.21; 7.23; 7.24; 11.1(e),( f),
                  (g) and (h); 11.3; 11.4; and 13;

                  (b)  Sections 3.2(b), (f) and (j) insofar as they are
                  excluded from the release under paragraphs 2.1(a)(i),
                  (ii) or (iii) of this Agreement and Release; and

                  (c)  Sections 11.1(a), (b), (c) and (d) insofar as they
                  relate to Claims that are excluded from the release


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                  hereunder pursuant to paragraph 2.1(a)(xi), 2.2(a) or
                  2.2(b) of this Agreement and Release.

             3.   Each of Thermo and Thermo Electron understands and
        acknowledges that it is possible that unknown losses or claims
        exist or that the Asserted Claims may have been underestimated in
        amount or severity, and the parties explicitly took that into
        account in determining to enter into this Agreement and Release,
        and nonetheless bargained, with the knowledge of the possibility
        of such unknown claims to provide for a full accord, satisfaction
        and discharge of all such claims that are within the scope of the
        release provided hereunder.  Consequently, each of Thermo and
        Thermo Electron expressly waives all rights under California
        Civil Code Section 1542, or any similar provision law.  Section
        1542 provides that:

                  " A general release does not extend to claims which the
                  creditor does not know or suspect to exist in his favor
                  at the time of executing the release, which if known by
                  him must have materially affected his settlement with
                  the debtor."


             4.   Each of Thermo and Thermo Electron represents, warrants
        and covenants that there are not now pending and that it will not
        hereafter under any circumstances commence or prosecute any suit,
        action or proceeding or assert any claim against any of the
        Releasees with respect to any Claim released hereunder.

             5.   Each of Thermo and Thermo Electron represents and
        warrants that:

                  (a)  it has not heretofore assigned or transferred or
                  purported to assign or transfer to any person or entity
                  any Claim (or portion thereof or interest therein)
                  released hereunder, and it shall indemnify, defend and
                  hold the Releasees harmless from and against any and
                  all claims based on or arising out of any such
                  assignment or transfer, or purported assignment or
                  transfer, of any such Claim or any portion thereof or
                  interest therein;

                  (b)  it has not been induced to execute this Agreement
                  and Release by any warranty, representation, promise,
                  covenant or agreement made by or on behalf of Releasees
                  or any other person or entity, other than the payment
                  of the Settlement Funds as described in paragraph 1
                  hereof;

                  (c)  it has carefully read and understood the scope and
                  effect of every provision of the Agreement and Release,
                  it has consulted with counsel of its choice who has
                  fully and completely explained to it the terms and

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                  provisions of this Agreement and Release and it has
                  executed this Agreement and Release voluntarily and
                  intending to be legally bound hereby;

                  (d)  it has full power and authority to execute and
                  deliver this Agreement and Release and to perform its
                  obligations hereunder in accordance with their terms;

                  (e)  the execution and delivery of this Agreement and
                  Release, and the performance by it of its obligations
                  hereunder, have been duly authorized by all necessary
                  corporate actions on its part;


                  (f)  this Agreement and Release constitutes its legal,
                  valid and binding obligation, enforceable against it in
                  accordance with the terms hereof.

             6.   This Agreement and Release constitutes a full and
        complete compromise and settlement of all Claims released
        hereunder.  In addition, Fisons acknowledges and agrees that this
        Agreement and Release constitutes a full and complete compromise
        and settlement of (i) the adjustments under Section 4.1 of the
        Agreement based on the Draft Closing Balance Sheet and the
        Closing Balance Sheet (as those terms are defined in the
        Agreement); and (ii) all of Fisons' rights and Thermo's
        obligations under Section 7.16 of the Agreement.

             7.   Each of Thermo and Thermo Electron acknowledges that
        this Agreement and Release, the settlement reflected herein and
        the payment made pursuant hereto are the result of the compromise
        resolution of disputed claims and shall never be offered or
        construed as an admission of any liability of any Releasee, or an
        acknowledgment of the validity of any Claim released hereunder,
        or as evidence of any such matter.  Releasees specifically deny
        any and all such liability or other responsibility to Releasors
        and the validity of any and all such Claims.

             8.   This Agreement and Release and all of its covenants,
        agreements, representations, warranties, terms and conditions
        shall be binding upon and shall insure to the benefit of (1) the
        successors, heirs and assigns hereafter of each of the parties
        hereto, and (2) any persons  and/or entities that acquire all or
        part of the assets of any of the parties hereto.

             9.   No waiver or compromise of any default under or breach
        of this Agreement and Release or any indulgence granted with
        respect to the performance of any obligation hereunder shall
        constitute or be deemed to imply a waiver of (1) any subsequent
        breach of this Agreement and Release or (2) the strict
        performance of any further obligations hereunder.

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             10.  This Agreement and Release sets forth the entire
        agreement between the parties and fully supersedes any and all
        prior agreements, representations and understandings between the
        parties hereto pertaining to the subject matter hereof.  No
        change, modification or addition, amendment or supplement to this
        Agreement and Release shall be valid unless set forth in writing
        and signed and dated by each and all of the parties hereto.

             11.  This Agreement and Release shall be governed by and
        construed in accordance with the laws of the State of New York
        (without regard to principles of conflicts of law).

             12.  This Agreement and Release may be executed in separate
        counterparts.


             IN WITNESS WHEREOF, the parties have caused this Agreement
        and Release to be executed by their duly authorized
        representatives as of the date first set forth above.

        Fisons plc                    Thermo Instrument Systems Inc.

        By:    /s/ Guillaume Prache   By:    /s/ Earl R. Lewis

        Name:  Guillaume Prache       Name:  Earl R. Lewis

        Title: Sr. Vice President     Title: President                   
               and Chief Financial
               Officer

                

                                      Thermo Electron Corporation

                                      By:    /s/ Earl R. Lewis

                                      Name:  Earl R. Lewis


                                      Title: Vice President

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        RHONE-POULENC RORER

        RHONE-POULENC RORER INC.
        500 ARCOLA ROAD
        P.O. BOX 1200
        COLLEGEVILLE, PA 19426-0107
        TEL. 610-454-8000




                                           December 15, 1997

        Thermo Instrument Systems Inc.
        81 Wyman Street
        Waltham, MA 02251

             Re:  Guarantee (the "Guarantee") of Rhone-Poulenc Rorer Inc.
                  ("RPR"), dated March 29, 1996, with respect to Asset
                  and Stock Purchase Agreement (the "Agreement") dated as
                  of March 29, 1996 among Thermo Instrument Systems Inc.,
                  Thermo Electron Corporation and Fisons plc

        Gentlemen:

             This will confirm that RPR as Guarantor under the
        above-referenced Guarantee acknowledges and consents to the
        revisions to the Agreement made by the Agreement and Release,
        dared as of December 15, 1997, between Fisons plc, Thermo
        Instrument Systems Inc. and Thermo Electron Corporation.

                                           Very truly your,

                                           RHONE-POULENC RORER INC.


                                           By: /s/ Richard B. Young
                                                Richard B. Young
                                                Vice President