142 Transadions of the [lT^,r^'^.Z%t 



larger and larger pencil ; this being an essential to obtaining higher 

 and higher defining power. 



" After succeeding fairly in a trial combination with this view, I 

 left the subject for a while, hoping it would be pursued by opticians. 

 But the glasses produced by the makers continued to be on the first 

 simple construction of two or three plano-convex compound lenses 

 till the beginning of 1837. At that time I called on Andrew Koss 

 regarding some object-glasses he had made to a microscope for 

 Richard Owen; when he told me he had been long engaged in 

 unsuccessful trials for a new construction. And at his request I 

 gave him a projection for a |^-inch objective of three compound 

 lenses, the front one a triple, which he soon worked out successfully, 

 and it became the standard form for high power for many years. 



" For lower powers I suggested at the same time a double 

 combination, and, borrowing of him a lens from among his former 

 failures, acd applying it in front of one of my own at home, 

 obtained at once the performance required. 



" It was natural that A. Ross should regard these as trade secrets ; 

 and accordingly, in his article on the Microscope in the ' Penny 

 Cyclopaedia ' he does not mention them, giving only the earlier con- 

 struction of my article in the ' Transactions.' The same is given 

 afterwards in the treatise which J. Quekett asked at the point of 

 its publication to dedicate to me ! And I did not feel required to 

 disclose A, Ross's secrets. After a while, witli his consent, I instructed 

 James Smith, 1840, to execute the same construction for inch and 

 half-inch glasses. Even in 1843 it was with the understanding that 

 he should not go to deeper powers than ^[-inch, and ' Smith's quarters ' 

 were long in repute. In these projections the endeavour was to 

 keep the angle of pencil at each surface of the glasses as moderate as 

 was consistent with the other essentials ; and by degrees the pencil 

 admitted has been enlarged beyond my expectations. Some varia- 

 tions too have been since made in the construction in which I have 

 had no part ; but for aU, the principle of the two aplanatic foci has 

 furnished the clue." 



I believe I am correct when I state that in foreign microscopes 

 also, object-glasses of high powers and fine performance are con- 

 structed on the same principle. And thus it seems not too much 

 to say, as has been lately said by a Professor in one of oiu- Univer- 

 sities — the son of one who was formerly associated with my father 

 through a common love of science — that he was " the pillar and 

 source of all the microscopy of the age." 



Although in this notice I have confined myself chiefly to mat- 

 ters connected with the microscope, it is right that I should add 

 that these were far from fonning the exclusive occupation of his 

 leisure hours. The comprehensive grasp of his intellect and the 

 extent and variety of his attainments were as remarkable as the 



