Exhibit 10.1

     THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER THE
     SECURITIES ACT OF 1933, AS AMENDED (THE "ACT").  THESE SECURITIES HAVE
     BEEN ACQUIRED FOR INVESTMENT, AND NOT WITH A VIEW TO DISTRIBUTION OR
     RESALE, AND MAY NOT BE SOLD, PLEDGED, MORTGAGED, HYPOTHECATED OR
     OTHERWISE TRANSFERRED (1) WITHOUT AN EFFECTIVE REGISTRATION STATEMENT
     UNDER THE ACT COVERING THESE SECURITIES OR (2) UNLESS AN EXEMPTION FROM
     REGISTRATION IS AVAILABLE.



                         THERMO INSTRUMENT SYSTEMS INC.
                       Promissory Note Due March 26, 1999
                             Waltham, Massachusetts

                                                              March 27, 1997


          For value received, Thermo Instrument Systems Inc., a Delaware
     corporation (the "Company"), hereby promises to pay to Thermo Electron
     Corporation (hereinafter referred to as the "Payee"), or registered
     assigns, on March 26, 1999, as described below, the principal sum of
     two hundred and ten million dollars ($210,000,000) or such part thereof
     as then remains unpaid, to pay interest from the date hereof on the
     whole amount of said principal sum remaining from time to time unpaid
     at a rate per annum equal to the rate of the Commercial Paper Composite
     Rate as reported by Merrill Lynch Capital Markets, as an average of the
     last five business days of the fiscal quarter, plus twenty-five (25)
     basis points, such interest to be payable in arrears on the first day
     of each fiscal quarter of the Company during the term set forth herein,
     until the whole amount of the principal hereof remaining unpaid shall
     become due and payable, and to pay interest on all overdue principal
     and interest at a rate per annum equal to the rate of interest
     announced from time to time by The First National Bank of Boston at its
     head office in Boston, Massachusetts as its "base rate" plus one
     percent (1%).  Principal and all accrued but unpaid interest shall be
     repaid on March 26, 1999.  Principal and interest shall be payable in
     lawful money of the United States of America, in immediately available
     funds, at the principal office of the Payee or at such other place as
     the legal holder may designate from time to time in writing to the
     Company.  Interest shall be computed on an actual 360-day basis.

          This Note may be prepaid at any time or from time to time, in
     whole or in part, without any premium or penalty.  All prepayments
     shall be applied first to accrued interest and then to principal.

          The then unpaid principal amount of, and interest outstanding on,
     this Note shall be and become immediately due and payable without
     notice or demand, at the option of the holder hereof, upon the
     occurrence of any of the following events:
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               (a)  the failure of the Company to pay any amount due
          hereunder within ten (10) days of the date when due;

               (b)  any representation, warranty or statement made or
          furnished to the Payee by the Company in connection with this Note
          or the transaction from which it arises shall prove to have been
          false or misleading in any material respect as of the date when
          made or furnished;

               (c)  the failure of the Company to pay its debts as they
          become due, the insolvency of the Company, the filing by or
          against the Company of any petition under the U.S. Bankruptcy Code
          (or the filing of any similar petition under the insolvency law of
          any jurisdiction), or the making by the Company of an assignment
          or trust mortgage for the benefit of creditors or the appointment
          of a receiver, custodian or similar agent with respect to, or the
          taking by any such person of possession of, any property of the
          Company;

               (d)  the sale by the Company of all or substantially all of
     its assets;

               (e)  the merger or consolidation of the Company with or into
          any other corporation in a transaction in which the Company is not
          the surviving entity;

               (f)  the issuance of any writ of attachment, by trustee
          process or otherwise, or any restraining order or injunction not
          removed, repealed or dismissed within thirty (30) days of
          issuance, against or affecting the person or property of the
          Company or any liability or obligation of the Company to the
          holder hereof; and

               (g)  the suspension of the transaction of the usual business
     of the Company.

          Upon surrender of this Note for transfer or exchange, a new Note
     or new Notes of the same tenor dated the date to which interest has
     been paid on the surrendered Note and in an aggregate principal amount
     equal to the unpaid principal amount of the Note so surrendered will be
     issued to, and registered in the name of, the transferee or
     transferees.  The Company may treat the person in whose name this Note
     is registered as the owner hereof for the purpose of receiving payment
     and for all other purposes.

          In case any payment herein provided for shall not be paid when
     due, the Company further promises to pay all cost of collection,
     including all reasonable attorneys' fees.




          No delay or omission on the part of the Payee in exercising any
     right hereunder shall operate as a waiver of such right or of any other
     right of the Payee, nor shall any delay, omission or waiver on any one
     occasion be deemed a bar to or waiver of the same or any other right on
     any future occasion.  The Company  hereby waives presentment, demand,
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     notice of prepayment, protest and all other demands and notices in
     connection with the delivery, acceptance, performance, default or
     enforcement of this Note.  The undersigned hereby assents to any
     indulgence and any extension of time for payment of any indebtedness
     evidenced hereby granted or permitted by the Payee.  

          This Note shall be governed by and construed in accordance with,
     the laws of the Commonwealth of Massachusetts and shall have the effect
     of a sealed instrument.


                                   THERMO INSTRUMENT SYSTEMS INC.



                                     By: __________________________________
                                        Arvin H. Smith
                                        Chairman and Chief Executive Officer

     [Corporate Seal]

     Attest:



     ____________________________
     Sandra L. Lambert
     Secretary




     cc:  Terry Dudding
          Seth Hoogasian
          Maureen Jacobs
          Sandra Lambert
          Karen Levin
          Andy Pilla
          Gina Silvestri
          Chris Vinchesi