SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, DC 20549

---

SCHEDULE 13D
(Rule 13d-101)

INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT
TO RULES 13d-1(a) AND AMENDMENTS THERETO FILED PURSUANT TO
RULE 13d-2(a)
(Amendment No. 3)¹

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of Rule 13d-1(e), 13d-1(f) or 13d-1(g), check the following box o.

          Note. Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See Rule 13d-7 for other parties to whom copies are to be sent.

(Continued on the following pages)

---

     ¹ The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.

     The information required in the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

---

---

---

     Unless indicated otherwise, all items left blank remain unchanged and any items which are reported are deemed to replace or add to the existing items in the original Schedule 13D (as amended). All defined terms shall have the same meaning as previously ascribed to them in the original Schedule 13D (as amended), unless otherwise noted.

     Item 1.   Security and Issuer.

     Item 2.   Identity and Background.

     Item 3.   Source and Amount of Funds or Other Consideration.

     Item 4.   Purpose of Transaction.

     The following additional paragraph is added before the last paragraph of item 4 of Amendment No. 2 to Schedule 13D:

     Emerson, pursuant to a Purchase Agreement dated as of January 14, 2004, by and among Emerson, MKS Instruments, Inc., the other selling shareholders named therein, and the several underwriters named therein, sold 1,714,286 shares of Common Stock on January 21, 2004 and 257,143 shares of Common Stock on January 23, 2004. In each case such shares were held directly by Emerson.

     Item 5.   Interest in Securities of the Issuer.

     (a) For the purposes of Rule 13d-3 promulgated under the Exchange Act, Emerson may be deemed to beneficially own 20,812,739 shares of Common Stock, or approximately 39.2% of the outstanding shares of Common Stock.

     For the purposes of Rule 13d-3 promulgated under the Exchange Act, Astec may be deemed to beneficially own 8,963,389 shares of Common Stock, or approximately 16.9% of the outstanding shares of Common Stock.

     Emerson disclaims the existence of a group (pursuant to the Shareholder Agreement, Voting Agreement or otherwise) and the Reporting Persons are filing this Statement jointly pursuant to Rule 13d-1(k)(1) promulgated under the Exchange Act.

     Except as set forth in this Item 5(a), none of the Reporting Persons, and, to the best of the knowledge of each Reporting Person, any persons named in Schedule A or Schedule B hereto, owns beneficially any Shares.

     (b) By virtue of the relationship set forth under Item 2 of this Statement, Emerson may be deemed to have the sole power to vote or direct the vote and sole power to dispose or direct the disposition of 1,065,182 shares of Common Stock held by it directly and the shared power to direct the disposition of and vote of the 8,963,389 shares of Common Stock held by Astec.

     By virtue of the Voting Agreement, the details of which are set forth under Item 4 of this Statement, Emerson may be deemed to have the shared power to vote or direct the vote of the 10,784,168 shares of Common Stock held by the Stockholders as of January 23, 2004 for the limited purposes described in Item 4 of this Statement.

---

     Astec has the shared power to vote or direct the vote and the shared power to dispose or direct the disposition of the 8,963,389 shares of Common Stock held by it.

     (c) None of the Reporting Persons or any of the persons set forth in Schedule A or Schedule B has effected any transaction in the shares of Common Stock during the past 60 days.

     (d) Emerson and Astec each shall be entitled to receive dividends declared on their respective shares of Common Stock and proceeds from the sale of the shares of Common Stock.

     (e) Not applicable.

     Item 6.    Contracts, Arrangements, Understandings or Relationships with Respect to Securities of the Issuer.

     Item 7.    Material to be Filed as Exhibits.

Exhibit 1:		Joint Filing Agreement
Exhibit 2:		Agreement and Plan of Merger with respect to the Acquisition of the ENI Business dated as of October 30, 2001 between Emerson Electric Co. and MKS Instruments, Inc.2
Exhibit 3:		Shareholder Agreement dated as of January 31, 2002 among MKS Instruments, Inc. and Emerson Electric Co.3
Exhibit 4:		Voting Agreement dated as of October 30, 2001 between Emerson Electric Co. and John R. Bertucci, Claire R. Bertucci and certain other parties set forth in Schedule 1 to such Voting Agreement.4
Exhibit 5:		Joinder Agreement to the Voting Agreement dated as of December 14, 2001 by Robinson Hill L.P.5