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                                                                      EXHIBIT 18


                                                                   June 30, 2000

TO THE FORMER STOCKHOLDERS OF THERMEDICS INC.:

     We are very pleased to announce that the merger of Thermedics Inc. with and
into Thermo Electron Corporation was completed on June 30, 2000. Under the terms
of the merger, each share of common stock of Thermedics outstanding immediately
prior to the merger (except for those shares owned by Thermo Electron, held by
stockholders exercising dissenters' rights and held in Thermedics' treasury) was
converted into the right to receive 0.45 shares of the common stock, $1.00 par
value per share, of Thermo Electron, and cash in lieu of fractional shares.

     Complete instructions on the exchange of your Thermedics stock
certificate(s) for the shares of Thermo Electron, and cash in lieu of fractional
shares, described above are included in the enclosed Letter of Transmittal. In
general, you will need to do the following:

     1.   Complete the first page of the Letter of Transmittal by indicating
          your stock certificate number(s) and the number of Thermo Instrument
          shares represented by each certificate. In addition, complete and sign
          the substitute Form W-9 on page 7.

     2.   Sign, date and complete the third page of the Letter of Transmittal.
          Please complete page 2 if you are requesting special issuance or
          delivery instructions; in addition, please note that this will require
          a signature guarantee on page 3.

     3.   Send your completed Letter of Transmittal along with your original
          stock certificate(s) to EquiServe Trust Company, N.A., who is serving
          as the exchange agent, at one of the addresses set forth on the first
          page of the Letter of Transmittal. DELIVERY OF THE CERTIFICATE(S)
          SHALL BE EFFECTED, AND RISK OF LOSS AND TITLE TO THE CERTIFICATE(S)
          SHALL PASS, ONLY UPON DELIVERY OF THE CERTIFICATE(S) TO THE EXCHANGE
          AGENT. WE STRONGLY RECOMMEND THAT YOU SEND YOUR STOCK CERTIFICATES AND
          LETTER OF TRANSMITTAL BY CERTIFIED OR REGISTERED MAIL, RETURN RECEIPT
          REQUESTED AND POSTAGE PRE-PAID, OR BY A NATIONALLY RECOGNIZED
          OVERNIGHT COURIER SERVICE.

     Any questions you have regarding the exchange of your Thermedics shares
should be directed to EquiServe Trust Company, N.A. at one of the addresses or
the phone number set forth on the first page of the Letter of Transmittal.

     Alternatively, you have a right to demand a judicially determined appraisal
of the value of your shares. If you intend to consider exercising this right,
you should read the enclosed notice of appraisal rights carefully and promptly.
Failure to follow any of the requirements set forth therein in a timely manner
will result in a loss of such rights.


                                        SANDRA L. LAMBERT
                                        Secretary