544 OBITUARY NOTICE OF JOSEPH JACKSON LISTER 



thought could not be avoided. I therefore induced him to make for me one of 

 /o much thinner in proportion, and had the satisfaction to find its performance 

 very nearly equal to his best /q. In one respect, indeed, it is superior ; showing 

 when in good adjustment the reflection from a minute ball of mercury a bright 

 point in any part of the field, while in the -^ and — it is so shown only in a small 

 portion of the field near the centre, and in the rest has a bur shooting outwards.' 

 This bur, of which a sketch is given, is the first mention of the ' coma ' which 

 afterwards formed so important a subject of his investigations. The note goes 

 on to describe a suggestion for another combination, illustrated by drawings 

 of magnified views of the curves of the glasses, executed with his usual extreme 

 neatness and accuracy ; and it concludes with the words, ' tried many experi- 

 ments to ascertain the best means of correcting small errors in aberration.' 



The note from which these quotations are made is the first of a long series 

 of accounts of experiments, with remarks upon them, indicating an amount 

 of labour of which, as I never saw the papers before, and as the work was for 

 the most part done either before my birth or during my early childhood, I had 

 previously had no idea. The notes are beautifully arranged, and might well 

 be published just as he left them. I must, however, content myself with 

 mentioning, in chronological order, some of the most interesting of their contents. 



In 1826, after a description of Amici's reflecting microscope and an account 

 of its performance, I find further projections of object-glasses for Mr. Tulley, 

 followed by a drawing for the engraver to illustrate a description of Tulley's 

 microscope, published by that optician. A copy of this pamphlet has been 

 preserved, and the first page begins with this acknowledgement : ' Before 

 commencing the description of the microscope it will be proper to state that the 

 construction of the instrument and its apparatus was suggested and made from 

 original drawings by my friend, J. J. Lister, Esq., whose ingenuity and skill 

 in these matters are very generally acknowledged.' The chief novelties in this 

 instrument, besides the improved object-glasses, were the following : — 



Graduated lengthening tube to the body. The stage-fitting for clamping 

 and rotating the object. A subsidiary stage. A dark well. A large disc, 

 which would incline and rotate for opaque objects. A ground-glass moderator. 

 A glass trough. A live-box made with flat plate. A combination of lenses 

 to act as condenser under the object (apparently the first approach to the present 

 achromatic condenser) . The erecting-glass ; and the adaptation of Wollaston's 

 camera lucida to the eye-piece. 



The value of the erecting-glass for facilitating dissections under low powers 

 is, perhaps, even yet not sufficiently appreciated. 



The camera lucida had long been a favourite instrument with my father 



