EXHIBIT 10

   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.

                                 Thermedics Inc.
                      Promissory Note Due February 11, 1997
                             Waltham, Massachusetts

                                                             February 13, 1996

        For value received, Thermedics Inc., a Massachusetts corporation (the
   "Company"), hereby promises to pay to Thermo Electron Corporation
   (hereinafter referred to as the "Payee"), or registered assigns, on
   February 11, 1997, as described below, the principal sum of fifteen million
   dollars ($15,000,000) 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 February 11, 1997. 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:

        (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;
PAGE


        (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, 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.


                                        2PAGE

        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.

                                                THERMEDICS INC.



                                                By: John.W. Wood, Jr.
                                                    -----------------    
                                                    John W. Wood, Jr.
                                                    President


   [Corporate Seal]

   Attest:


   Sandra L. Lambert
   -----------------
   Sandra L. Lambert
   Clerk




   cc: Ron Burman
       Seth Hoogasian
       Maureen Jacobs
       Gary Jones
       Sandra Lambert
       Karen Levin
       Chris Vinchesi