Exhibit 10.4
                           MASTER REPURCHASE AGREEMENT


             AGREEMENT dated as of the 14th day of November, 1997 between
        Thermo Electron Corporation,  a Delaware corporation  ("Seller"),
        and  Thermo  Vision  Corporation,  a  Delaware  corporation  (the
        "Buyer").

        1.   Applicability

             From  time  to  time   Buyer  and  Seller  may   enter  into
        transactions in which Seller agrees to transfer to  Buyer certain
        securities and/or  financial instruments  ("Securities")  against
        the transfer of funds by Buyer, with a  simultaneous agreement by
        Buyer to transfer  to Seller such  Securities on demand,  against
        the transfer of funds by Seller.  Each such  transaction shall be
        referred to herein as  a "Transaction" and  shall be governed  by
        this Agreement, unless otherwise agreed in writing.

        2.   Definitions

             (a)  "Act of Insolvency",  with respect to either  party (i)
        the  commencement  by  such  party  as  debtor  of  any  case  or
        proceeding  under  any  bankruptcy,  insolvency,  reorganization,
        liquidation, dissolution or  similar law,  or such party  seeking
        the appointment  of a  receiver,  trustee, custodian  or  similar
        official for such party or any substantial part  of its property;
        or (ii) the commencement of  any such case or  proceeding against
        such party, or another seeking such an appointment,  which (A) is
        consented to or not timely  contested by such party,  (B) results
        in the entry of an order  for relief, such an appointment  or the
        entry of  an  order  having  a  similar effect,  or  (C)  is  not
        dismissed within 15  days; or (iii)  the making by  a party of  a
        general assignment  for the  benefit of  creditors;  or (iv)  the
        admission in writing by a party of such party's  inability to pay
        such party's debts as they become due; 

             (b)  "Additional Purchased Securities", Securities  provided
        by Seller to Buyer pursuant to Paragraph 4(a) hereof; 

             (c)  "Income", with respect to any Security at any time, any
        principal thereof  then payable  and all  interest, dividends  or
        other distributions thereon; 

             (d)  "Market Value", with  respect to  any Securities as  of
        any date, the  price for  such Securities on  such date  obtained
        from a generally recognized  source agreed to  by the parties  or
        the most recent closing  bid quotation from  such a source,  plus
        accrued Income to the extent not included therein (other than any
        Income transferred to Seller  pursuant to Paragraph 6  hereof) as
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        of such  date  (unless  contrary  to  market  practice  for  such
        Securities);

             (e)  "Other Buyers", third parties that have entered into an
        agreement with  Seller that  is   substantially  similar to  this
        Agreement; 

             (f)  "Pricing Rate", a  rate equal  to the Commercial  Paper
        Composite rate for 30-day  maturities provided by Merrill  Lynch,
        Pierce, Fenner  & Smith  Incorporated (or,  if such  rate is  not
        available, a substantially equivalent rate agreed to by Buyer and
        Seller) plus 25 basis  points,  which  rate shall be adjusted  on
        the first business  day of each  fiscal quarter  and shall be  in
        effect for the entirety such fiscal quarter;
         
             (g)  "Purchase  Price",   the  price   at  which   Purchased
        Securities are transferred by Seller to Buyer; 

             (h)  "Purchased Securities", the  Securities transferred  by
        Seller to Buyer  in a Transaction  hereunder, and any  Securities
        substituted therefor in accordance with Paragraph 9 hereof.   The
        term "Purchased Securities"  with respect  to any Transaction  at
        any  time  also  shall  include  Additional  Purchase  Securities
        transferred  pursuant  to  Paragraph   4(a)  and  shall   exclude
        Securities returned pursuant to Paragraph 4(b);  

             (i)  "Repurchase  Collateral   Account",  a   book   account
        maintained by  Seller  containing,  among other  Securities,  the
        Purchased Securities; and

             (j)  "Repurchase Price",  for  any  Purchased  Security,  an
        amount equal to the  Purchase Price paid  by Buyer to Seller  for
        such Purchased Security. 

        3.   Transactions

             (a)  A Transaction  may  be  initiated  by  Buyer  upon  the
        transfer of the Purchase  Price to Seller's  account.  Upon  such
        transfer, Seller  shall transfer  to  Buyer Purchased  Securities
        having a Market Value equal to 103% of the Purchase Price.

             (b)  Purchased Securities shall be held in custody for Buyer
        by Seller in  the Repurchase  Collateral Account.   Seller  shall
        indicate on its books for  such account Buyer's ownership  of the
        Purchased Securities.  Upon reasonable request from Buyer, Seller
        shall provide Buyer with a complete list of  Purchased Securities
        owned by Buyer.  

             (c)  Upon demand by Buyer or Seller, Seller shall repurchase
        from Buyer, and Buyer shall  sell to Seller,  for  the Repurchase
        Price all or any part  of the Purchased Securities then  owned by
        Buyer.

        4.   Margin Maintenance

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             (a)  If at  any  time  the  aggregate Market  Value  of  all
        Purchased Securities then owned by Buyer is less than 103% of the
        aggregate Repurchase Price  for such  Purchased Securities,  then
        Seller shall transfer to Buyer additional Securities ("Additional
        Purchased Securities"),  so that  the aggregate  Market Value  of
        such  Purchased   Securities,  including   any  such   Additional
        Purchased Securities, will  thereupon equal  or exceed   103%  of
        such aggregate Repurchase Price.

             (b)  If at  any  time  the  aggregate Market  Value  of  all
        Purchased Securities  then owned  by Buyer  exceeds  103% of  the
        aggregate Repurchase Price  for such  Purchased Securities,  then
        Seller may transfer Purchased  Securities to Seller, so  that the
        aggregate  Market  Value  of   such  Purchased  Securities   will
        thereupon not exceed 103% of such aggregate Repurchase Price.

        5.   Interest Payments

             If during any fiscal month Buyer owned Purchased Securities,
        then on the first day  of the next following fiscal  month Seller
        shall pay to Buyer  an amount equal to  the sum of the  aggregate
        Repurchase Prices of the  Purchased Securities owned by  Buyer at
        the close of each day  during the preceding fiscal  month divided
        by the number of days in such month and the product multiplied by
        the Pricing Rate times the  number of days in such  month divided
        by 360.

        6.   Income Payments and Voting Rights

             Where a particular Transaction's term extends over an Income
        payment  date  on  the  Purchased  Securities  subject   to  that
        Transaction, Buyer shall,  on the  date such  Income is  payable,
        transfer to  Seller an  amount equal  to such  Income payment  or
        payments with respect to any Purchased Securities subject to such
        Transaction.  Seller shall retain all voting rights  with respect
        to Purchased Securities sold to Buyer under this Agreement.

        7.   Security Interest

             Although the parties intend that all  Transactions hereunder
        be sales  and purchases  and not  loans, in  the  event any  such
        Transactions are deemed to  be loans, Seller  shall be deemed  to
        have pledged to Buyer as  security for the performance  by Seller
        of  its  obligations  under   each  such  Transaction  and   this
        Agreement, and  shall  be  deemed  to have  granted  to  Buyer  a
        security interest  in,  all  of  the  Purchased  Securities  with
        respect to all Transactions hereunder and all proceeds thereof.

        8.   Payment and Transfer

             Unless otherwise  mutually agreed,  all  transfers of  funds
        hereunder shall  be  in immediately  available  funds.   As  used
        herein with respect to Securities, "transfer" is intended to have

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        the  same  meaning  as  when   used  in  Section  8-313   of  the
        Massachusetts Uniform Commercial  Code or,  where applicable,  in
        any federal regulation governing transfers of the Securities.

        9.   Substitution

             Buyer hereby  grants  Seller  the authority  to  manage,  in
        Seller's  sole  discretion,  the  Purchased  Securities  held  in
        custody for Buyer by Seller in the Repurchase Collateral Account.
        Buyer expressly  agrees  that  Seller may  (i)  substitute  other
        Securities  for  any  Purchased  Securities  and  (ii)  commingle
        Purchased Securities with other Securities held in the Repurchase
        Collateral Account.  Substitutions  shall be made by  transfer to
        Buyer of  such other  Securities and  transfer to  Seller of  the
        Purchased Securities for which substitution is being made.  After
        substitution, the substituted  Securities shall  be deemed to  be
        Purchased Securities.    Securities  which  are  substituted  for
        Purchased Securities shall  have a  Market Value at  the time  of
        substitution equal to  or greater  than the Market  Value of  the
        Purchase Securities for which such Securities were substituted.

        10.  Representations

             Each of  Buyer and  Seller represents  and  warrants to  the
        other that (i) it is duly authorized to execute  and deliver this
        Agreement, to enter into the Transactions  contemplated hereunder
        and to  perform  its  obligations  hereunder and  has  taken  all
        necessary  action  to  authorize  such  execution,  delivery  and
        performance, (ii) the person signing this Agreement on its behalf
        is duly authorized to do so on its behalf, (iii)  it has obtained
        all  authorizations  of   any  governmental   body  required   in
        connection with this Agreement and the Transactions hereunder and
        such authorizations are  in full  force and effect  and (iv)  the
        execution, delivery  and performance  of this  Agreement and  the
        Transactions hereunder  will  not  violate  any  law,  ordinance,
        charter, by-law  or rule  applicable to  it or  any agreement  by
        which it is bound or by which any of its assets are affected.  On
        the date  for any  Transaction  Buyer and  Seller  shall each  be
        deemed to repeat all the foregoing representations made by it.

        11.  Events of Default

             In the event that  (i) Seller fails  to repurchase or  Buyer
        fails to transfer Purchased Securities upon demand for repurchase
        from either Buyer or Seller,  (ii)  Seller or Buyer  fails, after
        one business day's  notice, to  comply with  Paragraph 4  hereof,
        (iii) Buyer   fails  to  make payment  to Seller  pursuant  to   
        Paragraph 6 hereof, (iv) Seller fails to comply  with Paragraph 5
        hereof,  (v) an Act  of Insolvency occurs with respect  to Seller
        or Buyer, (vi) any representation  made by Seller or  Buyer shall
        have been incorrect or untrue  in any material respect  when made
        or repeated or  deemed to have  been made  or repeated, or  (vii)
        Seller or Buyer shall admit to the other its inability to, or its

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        intention not to, perform any of its obligations  hereunder (each
        an "Event of Default"):

             (a)  At the option of the nondefaulting party,  exercised by
        written notice to  the defaulting  party (which  option shall  be
        deemed to  have  been exercised,  even  if  no notice  is  given,
        immediately upon the occurrence of any Act of Insolvency), Seller
        shall become  obligated to  repurchase,  and Buyer  shall  become
        obligated to sell, all  Purchased Securities then owned  by Buyer
        for the Repurchase Price of such Purchased Securities.

             (b)  If Seller is the  defaulting party and Buyer  exercises
        or is  deemed  to  have  exercised  the  option  referred  to  in
        subparagraph (a) of this Paragraph, (i) the  Seller's obligations
        hereunder  to  repurchase  all   Purchased  Securities  in   such
        Transactions shall thereupon become immediately due  and payable,
        (ii) all Income paid after such exercise or deemed exercise shall
        be  retained  by  Buyer  and  applied  to  the  aggregate  unpaid
        Repurchase  Prices  owed  by  Seller,  and  (iii)   Seller  shall
        immediately deliver to Buyer any Purchased Securities  subject to
        such Transactions then in Seller's possession.

             (c)  In all Transactions  in which  Buyer is the  defaulting
        party,  upon  tender  by  Seller  of  payment  of  the  aggregate
        Repurchase Prices for all such Transactions, Buyer's right, title
        and  interest  in  all  Purchased  Securities  subject   to  such
        Transactions shall  be deemed  transferred to  Seller, and  Buyer
        shall deliver all such Purchased Securities to Seller.

             (d)  After one business day's notice to the defaulting party
        (which notice need  not be given  if an  Act of Insolvency  shall
        have  occurred,  and  which   may  be  the  notice   given  under
        subparagraph (a) of this Paragraph  or the notice referred  to in
        clause (ii)  of  the  first  sentence  of  this  Paragraph),  the
        nondefaulting  party may: 

                  (i)    as  to  Transactions  in  which  Seller  is  the
        defaulting party, (A) immediately sell, in a recognized market at
        such price or prices  as Buyer may reasonably  deem satisfactory,
        any or all Purchased Securities subject to such  Transactions and
        apply the  proceeds thereof  to the  aggregate unpaid  Repurchase
        Prices and any other amounts owing by Seller hereunder  or (B) in
        its sole discretion elect, in lieu of selling all or a portion of
        such  Purchased  Securities,  to  give  Seller  credit  for  such
        Purchased Securities in an amount equal to the  price therefor on
        such date, obtained  from a  generally recognized  source or  the
        most recent closing bid quotation from such a source, against the
        aggregate unpaid Repurchase Prices and any other amounts owing by
        Seller hereunder; and

                  (ii)    as  to  Transactions  in  which  Buyer  is  the
        defaulting   party,   (A)   purchase   securities   ("Replacement
        Securities") of  the  same  class  and amount  as  any  Purchased
        Securities that are not delivered by Buyer to  Seller as required

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        hereunder or  (B)  in  its  sole discretion  elect,  in  lieu  of
        purchasing Replacement Securities, to be deemed to have purchased
        Replacement Securities  at  the  price  therefor  on  such  date,
        obtained from a  generally recognized source  or the most  recent
        closing bid quotation from such a source.

             (e)  As to  Transactions in  which Buyer  is the  defaulting
        party ,  Buyer shall  be liable  to Seller  (i)  with respect  to
        Purchased   Securities   (other    than   Additional    Purchased
        Securities), for any excess of the price paid (or deemed paid) by
        Seller for Replacement  Securities therefor  over the  Repurchase
        Price for  such Purchased  Securities and  (ii)  with respect  to
        Additional Purchased Securities,  for the  price paid (or  deemed
        paid) by Seller for the Replacement Securities therefor.  

             (f)  The  defaulting   party   shall   be  liable   to   the
        nondefaulting party for  the amount  of all  reasonable legal  or
        other expenses incurred by the nondefaulting party  in connection
        with or as a consequence of an Event of Default.

             (g)  The nondefaulting party shall have, in addition  to its
        rights hereunder, any rights otherwise available to it  under any
        other agreement or applicable law.

        12.  Single Agreement

             Buyer and Seller acknowledge that, and have entered hereinto
        and will enter into  each Transaction hereunder in  consideration
        of and in reliance upon the fact that, all Transactions hereunder
        constitute a  single business  and  contractual relationship  and
        have been made in consideration of each other.  Accordingly, each
        of Buyer and Seller agrees (i) to perform all  of its obligations
        in respect of each Transaction  hereunder, and that a  default in
        the performance  of  any  such  obligations  shall  constitute  a
        default by it in respect of all Transactions hereunder, (ii) that
        each of  them shall  be  entitled to  set  off claims  and  apply
        property held  by  them in  respect  of any  Transaction  against
        obligations owing to  them in respect  of any other  Transactions
        hereunder and (iii) that payments, deliveries and other transfers
         made by either  of them in respect  of any Transaction shall  be
        deemed to have been made in consideration of payments, deliveries
        and  other  transfers  in  respect  of  any   other  Transactions
        hereunder,  and  the  obligations  to  make  any  such  payments,
        deliveries and other transfers may be applied against  each other
        and netted.

        13.  Entire Agreement; Severability

             This  Agreement  shall  supersede  any  existing  agreements
        between the parties containing  general terms and conditions  for
        repurchase  transactions.    Each  provision  and  agreement  and
        agreement herein  shall be  treated as  separate and  independent
        from any  other  provision  or  agreement  herein  and  shall  be

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        enforceable notwithstanding  the  unenforceability  of  any  such
        other provision or agreement.

        14.  Non-assignability; Termination

             The  rights  and  obligations  of  the  parties  under  this
        Agreement and under  any Transactions  shall not  be assigned  by
        either party  without  the prior  written  consent of  the  other
        party.    Subject  to  the  foregoing,  this  Agreement  and  any
        Transactions shall be binding upon and shall inure to the benefit
        of the parties and their respective successors and assigns.  This
        Agreement may be  canceled by  either party  upon giving  written
        notice  to  the   other,  except   that  this  Agreement   shall,
        notwithstanding   such   notice,   remain   applicable   to   any
        Transactions then outstanding.

        15.  Governing Law

             This  Agreement  shall  be  governed  by  the  laws  of  the
        Commonwealth  of  Massachusetts  without  giving  effect  to  the
        conflict of law principles thereof.

        16.  No Waivers, Etc.

             No express  or implied  waiver of  any Event  of Default  by
        either party  shall constitute  a waiver  of any  other Event  of
        Default and  no exercise  of any  remedy hereunder  by any  party
        shall constitute  a waiver  of its  right to  exercise any  other
        remedy hereunder.  No modification or waiver of  any provision of
        this Agreement  and  no  consent  by any  party  to  a  departure
        herefrom shall be  effective unless  and until such  shall be  in
        writing and duly executed by both of the parties hereto. 

        19.  Intent

             (a)  The  parties  recognize  that  each  Transaction  is  a
        "repurchase agreement" as that term is defined in  Section 101 of
        Title 11 of the United States Code, as amended (except insofar as
        the type of Securities subject to such Transaction or the term of
        such Transaction would render such definition  inapplicable), and
        a "securities contract" as that term is defined in Section 741 of
        Title 11 of the United States Code, as amended.

             (b)  It is understood that either party's right to liquidate
        Securities  delivered  to  it  in  connection  with  Transactions
        hereunder or to exercise any other remedies pursuant to Paragraph
        11 hereof, is a  contractual right to liquidate  such Transaction
        as described in Sections  555 and 559 of  Title 11 of the  United
        States Code, as amended.

             IN WITNESS WHEREOF, the parties have executed this Agreement
        as of the date first above written.

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        THERMO ELECTRON CORPORATION        THERMO VISION CORPORATION


        By:        /s/John N. Hatsopoulos
           ------------------------------------------------
        By:        /s/Kristine S. Langdon
           ------------------------------------------------
             John N. Hatsopoulos               Kristine S. Langdon
             Title:    President               Title:    President