30 Life of John Dollond, F.R.S. 



Mr. Dollond's celebrity in optics became now unlvers<Al ; 

 and the friendship and protection ot" the most eminent men 

 of science flaltered and encouraged his pursuils. To enu- 

 merate the persons, both at home and abroad, who dislin- 

 guislied him by their correspcidence or CHltivated his ac- 

 (piaintance, however honourable to his memory, wovdd 

 only be an empty praise. We cannot, however, forbear 

 juentioning ihe names of a few persons, who held the 

 highest place in his esteem as men of worth and learning : 

 Mr. Thomas Simpson, master of the Royal Academy at 

 Woolwich; Mr. Harris, assay-master at the Tower, v/ho 

 was at that time engaged in wiiting and publishing his 

 Treatise on Optics ; the" Rev. Dr. Braciley, then astronomer 

 royal ; the Rev. William Ludlow, of St. .John's college, 

 Cambridge; Mr. John Canton, a most mgenious man, and 

 celebrated not less for his knowledge in natural philosophy, 

 than for his neat and accurate manner of nuiking philoso- 

 phical experiments. To this catalo^rtic of the philosophical 

 names of those days, we must add that of the orcsent 

 astronomer royal, the Rev. Dr. Ma^kelyne, whose labours 

 have so emin.nlly benefited the science of astronomy. 



Surrounded by these enlightened men, in a state of mind 

 prepared for tlie severest investigation of philosophic truths, 

 and in circumstances favourable to liberal UKjuiry, Mr. 

 Dollond engaged in the discussion of a subject, which at 

 that time not only interested this country, but all iLurope. 

 Sir Isaac Newton had tleelared, in his Treatise on Optics, 

 page 112, " That all refracting substances diverged the 

 prismatic colours in a constant proportion to their mean 

 refraction;" and drew this conclusion, " that refraction 

 could not be produced without ce>lour ;" and, consequently, 

 *' that no improvement could he expected in the refracting 

 telescope." No one doubted the accuracy with which Sir 

 Isaac Newton had made tlie experunent ; yet some men, 

 particularly M. luder and oth-rs, were of opinion that the 

 conclusion which Newton had drawn from it went too far, 

 and maintained that in very small angles refraction might 

 be obtained without colour. Mr. DcrUcnd was not of that 

 opi)iion, but defended Newton's doctrine with much learn- 

 ing and ingenuity, as may be seen by a reference to the 

 letters wliich passed between Eulci and Dollond upon that 

 occasion, and which were pu')lished in the Phil. Trans, 

 vol. xlviii. page 2S7. and contended ihat, <■' If the result of 

 the exi)eriment had been as described by Sir Isaac New- 

 ton, there could not be refraction without colour." 



A mind constituted like Mr. Doljond's could not re- 

 main 



