Royal Society, 1 39 



in 1804, he laid before the Royal Society of Edinburgh the careful 

 and elegant experiments, by which he demonstrated that the pro- 

 position laid down by Dr. Croune in 1683 regarding the expansion 

 of water by cold is really correct ; and that the phenomena observed 

 do not depend, as Hooke and others had maintained, on changes 

 occumng in the capacity of the vessel in which the experiment is 

 conducted. From these researches, Dr. Hope concluded that the 

 maximum density of water is at 39^° or 40^^ Fahr. ; a result con- 

 firmed by the more recent and very accurate experiments of Hiill- 

 Strom, who estimates its point of greatest density at 39*39° Fahr. 

 This, his favourite subject, received a still further elucidation from 

 him at a later period of his life. In 1839 he read to the Royal 

 Society of Edinburgh a paper, in which he showed that this law held 

 true with regard to water only in its pure state ; and that when it 

 contains saline matters in solution, as in sea-water, it follows the 

 ordinary law of regularly progressive expansion by heat and con-i- 

 tractlon by cold. 



The last communication which Dr. Hope made to the chemicall' 

 world was in 1843, when he read two papers on the colouring mat-' 

 ter of the Camellia japonica, Magnolia yrandijlora., and Chrysau' 

 themum leucanthemum. In these communications, he asserted the 

 existence of three new proximate organic bodies, to which he gave 

 the names of Camelline, Magnoline and Leucanthemine, but which 

 he did not obtain in a separate form. :\v v.- iv^xjij-.i 



Dr. Hope's claims on the gratitude of the chemical world arer not 

 to be estimated by his merits as an observer. He seems, from the first, 

 to have resolved to devote himself rather to the business of teaching 

 than of research. He spared no pains to make his lectures attractive 

 to the student; his style of writing was elegant and concise, and hia'; 

 delivery easy but impressive. The great charm of his lectures, how« '^ 

 ever, consisted in the elegant experiments with which he illustrated 

 them : these were so well-devised, so skilfully arranged and so neatly 

 performed, that a failure on his lecture-table was an occurrence 

 almost unknown. One other circumstance which contributed to his 

 success as a lecturer was the excellent health which he enjoyedV 

 During a period of nearly sixty years, in which he was engaged iw'^ 

 studying or teaching medicine and chemistry, he was not more than 

 six days in all prevented by illness from discharging his duties. He 

 retained his vigour and his- faculties with little diminution till within 

 a short period of his death]; but in 1843, finding himself unequal to 

 the duties of his class, he arranged with his colleague Dr. Traill ttt>f! 

 deliver the lectures for him, and shortly after resigned the appointM^^d 

 ment into the hands of the patrons. y- ub 



Dr. Gregory was appointed to the vacant chair, and before he had 

 entered on its duties his veteran predecessor died at Edinburgh on 

 the 13th of June 1844, in the 78th year of his age. ; -i 



John Dalton was born on the 5th of September, 1766, at Eagles^ 

 field, near Cockermouth, in the Cumberland Lake district. He >. 

 passed some years as teacher of mathematics in a school at Kendal^ IjI 



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