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                                                                      EXHIBIT 18

                                              June 30, 2000

TO THE FORMER STOCKHOLDERS OF THERMO INSTRUMENT SYSTEMS INC.:

     We are very pleased to announce that the merger of Thermo Instrument
Systems 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 Thermo
Instrument outstanding immediately prior to the merger (except for those shares
owned by Thermo Electron, held by stockholders exercising dissenters' rights and
held in Thermo Instrument's treasury) was converted into the right to receive
0.85 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 Thermo Instrument 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 Thermo Instrument
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