D O C U M E N T 1 7 5 A P R I L 1 9 2 8 3 0 1 The quartz plate with the particle imbedded in its surface would be cleaned in the same way as is usual in ultra-microscopy. As regards the biological section, this could be prepared immediately before use. But, in fact, the method I have thought of for securing a plane surface in the section would also serve to remove a surface- film from it. ALS. [20 633] and [20 634]. [1] Synge (1890–1957) was a private scholar living near Dublin. [2] The date is written in another hand, neither Synge’s nor Einstein’s. It is presumably correct given the date of Einstein’s reply (Doc. 182). [3] Synge had previously corresponded with Einstein concerning his efforts to publish an edition of Hamilton’s works, which Einstein supported (see Einstein to Synge, 4 May 1922 [Vol. 13, 178a, in Vol. 14] in reply to a letter from Synge of 16 April, which is not available, and Synge to Einstein, 10 May 1922 [Vol. 13, Doc. 187]). [4] John Lighton Synge (1897–1995), Professor of Natural Philosophy at Trinity College, Dublin, and Arthur William Conway (1875–1950), Professor of Mathematical Physics at University College Dublin. [5] Hamilton 1931. [6] Essentially the Royal Irish Academy refused to undertake the project at Edward’s urging. Even- tually, though, he persuaded his brother John to involve himself. As the latter became a member of the Academy’s council in 1927, he succeeded where his brother had failed. In the meantime, perhaps inspired by his physicist brother and the topic of the first volume of Hamilton’s papers, Edward H. Synge had taken up his own theoretical research in optics, to which the remainder of the letter is devoted (see Florides 2008, p. 413). [7] A discussion of this planing technique is given in Synge 1928, pp. 359–360. [8] Carl Zeiss AG was an optics firm based in Jena, Germany. [9] A condenser is a type of a lens commonly situated in microscopes under the object. It focuses light strongly upon the object to illuminate it for viewing from above. [10] Numerical Aperture. [11] The proposal outlined here, of using light scattered off a small particle, today forms the basis of aperture-less near-field microscopy, as described in Novotny 2007, pp. 146–147. [12] Synge describes the technique of dark-field microscopy (then called ultramicroscopy), invented by the Austrian-Hungarian chemist Richard Adolf Zsigmondy in 1902 (Novotny 2007, p. 143). [13] Captions: “objective of microscope” “quartz cover glass” “biological sample fixed to cover glass” “colloidal particle” quartz slide” “cardioid condenser.” [14] Probably the first description of the technique of scanning in microscopy (McMullan 1990 and Novotny 2007). [15] Adam Hilger Ltd. [16] At this time the most familiar use of the technique of imaging by two-dimensional scanning was in facsimile (or fax) machines, then often known as phototelegraphy. [17] The method is discussed in Synge 1928. [18] Caption: “particle.” [19] Photo-electric. [20] Otto Richard Lummer (1860–1925) was one of the developers of the mercury vapor lamp. [21] John William Strutt, 3rd Baron Rayleigh (1842–1919). The reference is probably to his papers on Rayleigh scattering (Rayleigh 1871a, b, and c).