Richard Waller wrote Letter L-234 to Leeuwenhoek, asking him to examine the colors of birds' feathers and other bodies, such as silk, paint, and mercury and whether he had observed sperm inside of an egg
Text of the letter in Alle de Brieven / The Collected Letters at the DBNL - De Digitale Bibliotheek voor de Nederlandse Letteren.
The date is New Style, which was ten days ahead of the Old Style date of 31 January 1694 used by Waller in London. Leeuwenhoek had not yet received it when, two days later on 12 February 1694, he sent Letter L-235 to Waller asking whether the Society had received Leeuwenhoek's Letter L-233 of 24 January 1694.
Waller acknowledged receipt of two letters from Leeuwenhoek. He asked Leeuwenhoek to look microscopically at the colors not only of birds' feathers but of:
other coloured bodys; possibly the same thread of silke, dyed of different colours, might be examined to see what alteration is made in the outward or inward parts therof, wch causes that different reflexion of Light giving those colours; possibly painters Colours may be fit subjects, and possibly the several disguises of Mercury in white, red, yellow and the like might give different appearances of ye constituent parts in the microscope, which I leave to yr choice
He also inquired whether Leeuwenhoek had observed sperm inside of an egg.
Letter Book Original, vol. XI, part I, pp. 205-206.
