Updated February 11, 2005
Sources - Page 2
The Bryant Library, 2 Paper Mill Road, Roslyn, New York 11576.
Two extensive Clarence Mackay related collections reside here.
     1. The Mackay Family Scrapbook Collection: 1898-1924 (50 professionally assembled volumes available on microfilm)
     2. The Charles Hechler Collection (Estate superintendent 1907-1938) donated in 1995 by Ken Hechler.

Truman Presidential Museum & Library.  Independence, Missouri.
Oral History Interview with Ken Hechler, by Niel Johnson, 1985 (short item concerning growing up on the Mackay Estate in Roslyn)

University Library, University of Nevada Reno.  Reno, Nevada.
"The Life of Clarence Hungerford Mackay," copyrighted, unpublished paper by Robert M. Hawkins, 1961 (son of Katherine Mackay Hawkins and grandson of Clarence H. Mackay).
    Best secondary sources I've found for insight into the Mackay art and armor collections and his cable-telegraph business.

"Fortune", Vol. 11, No. 6, December 1930, "IT&T" (Behn Brothers, Company, Maps, Directors)

"International Studio", Vol. LXXXI, Number 339, August 1925, pp. 335-345. V.R. Valentiner, "The Clarence H. Mackay Collection". (Stages of development in Italian art of the Early Renaissance. Paintings from the period 1430-1505)

Ibid, Vol. LXXXIV, Number 351, August 1926, pp. 39-45.  George Leland Hunter, "Clarence H. Mackay's Gothic Tapestries".

Ibid, Vol. XCIV, Number 391, December 1929, pp. 29-34.  Royal Cortissoz, "The Clarence H. Mackay Collection". (A group of paintings representing many categories of the Italian tradition from Gothic origin to the high Renaissance)

"Postal Telegraph", January 1910, "The Twenty Fifth Anniversary Speech of President Mackay, New York"

Ibid, June 1924, "The Fourtieth Anniversary Speech of President Mackay, New York, May 10, 1924"

"The AWA Review", Vol. 8 (Bloomfield, NY: Antique Wireless Association, 1993), pp. 74-107. Hank Olson and Bill Orr, "The KFS-Federal-Mackay Story: From CW Arc to Silicon Valley, the Waves of Progress"

"Time Magazine", April 2, 1928, Business & Finance, "International Communications". (Behn's ITT merger with the Mackay companies)(Clarence Mackay: "less the director of 58 corporations than the member of 27 clubs")(aim of merger - to better position ITT to compete with Western Union and Britain's supremacy in world communications - Eastern Telegraph Company and the Marconi Company of London)

Ibid, March 27, 1933, Art, "Agony in the Garden". (Mackay sale of art and closing mansion)

Ibid, February 25, 1935, Art, "Swordsmith". (Armor and Arms Club)

Ibid, May 27, 1935, People, "Names make news". (Mackays reopening mansion)

Ibid, June 24, 1935, Business & Finance, "Postal Down". (Postal partitions for permission to reorganize under the Bankruptcy Act)

Ibid, February 12, 1940, Business & Finance, "Parceled Postal". (Postal Inc. and American Cable & Radio Corp.)(Postal free of ITT but cedes cable and radio properties to A.C. & R.)
    A great deal of information resides in newspapers of the day but finding the detail is slow, tedious work.  The New York Times is the best cataloged and most readily available newspaper collection.

New York Times, November 14, 1938.  Obituaries  "Clarence Mackay Dies At Home Here".

New York Times, December 7, 1938. "Mackay's Widow To Get $2,050,000".

New York Tribune, July 27, 1902.  Sunday Supplement  "The New Head of the Mackay Family, Clarence H., Combines Good Business Ability With A Love For Horses".

Roslyn News, September 24, 2004. "Thousands Turn Out for Groundbreaking Festivities".