Please return this paper
French weight English grain 1. gramme = 15.44 1. milligramme = 0.0154
Now how many milligrammes (to one place of decimals) does one English grain equal?
- f1 4451f.f1The date is conjectured by the relationship of this letter to a note in DAR 157.1: 70, dated [circa 31 March 1864], in which it was first recorded that pieces of thread, weighed in grains, were placed on specimens of Clematis. Emma Darwin recorded in her diary (DAR 242) that the `Boys', presumably including George, went back to school on 5 April 1864; they were at home for the Easter holidays (see letter from H. E. Darwin to W. E. Darwin, [16 March 1864], n. 3). In 1864, Easter Sunday was 27 March. See letter to J. D. Hooker, 5 April  and n. 17, and n. 3, below. The letter was found in the folio containing CD's notes on climbing plants.
- f2 4451f.f2CD wrote this phrase in pencil, probably as an afterthought. On the back of the letter is a note in ink: `I'm very sorry I forgot to Send it before | G. HD'; George may have forgotten to return this letter with his letter of [after 6 April 1864?]. CD occasionally made use of George's mathematical skills (see, for example, Correspondence vol. 11, letter from G. H. Darwin, [before 11 May 1863]).
- f3 4451f.f3In March or April 1864, CD began weighing in grains the inches of thread that he tied to the petioles of some of the leaf-climbing Clematis species to test their sensitivity (see `Climbing plants', pp. 27--8, 29, 31, 33--4; see also letter to J. D. Hooker, 5 April  and n. 17). CD's notes on these experiments are in DAR 157.1: 62--3, 70--1, 73--5, and 77. CD had been told the number of English grains in a gram several years earlier, when he was researching substances that he was applying to the insectivorous sundew, Drosera (see Correspondence vol. 8, letter from Edward Cresy, 10 November 1860).