434 Notes. 



bition of 1851 ; but we are unable to obtain any information on the 

 subject from the Report of the Jurors of the Microscopical section. 

 This was the last Microscope Andrew Ross designed. He died in 

 1859, and was succeeded by his son, Thomas Ross. 



Thomas Ross prepared for the Exhibition of 1862 a new model 

 very similar to the previous one, the chief difference being the addition 

 of a binocular body, fig. 116. This form of binocular, which was 

 invented by Wenham in Dec. 1860, is by far the best of all the con- 

 trivances that have as yet been introduced. The stage was made a 

 little thinner, and the diameter of the substage tube was altered from 

 2 in. to 1-527 in. 



On March 15th, 18-43, Rosa delivered the Microscope which had 

 been ordered by the Microscopical Society of London on May 26th, 

 1841 ; but unfortunately we are now unable to determine what that 

 Microscope was like, because it was exchanged in 1863 for the bino- 

 cular Microscope in our cabinet, which was made by Thomas Ross, 

 tig. 116. The original Andrew Ross model must have been like 

 either fig. 113 or fig. 114. If we assume that it was like the latter 

 figure, which was then an entirely new pattern, some time must have 

 been taken with alterations and adjustments, and so the delay in its 

 delivery would be accounted for. 



THE OBJECT-GLASSES OF ANDREW KOSS. 



The first achromatic Microscope object-glass constructed in this 

 country was made to the order of Dr. Goring by W. Ttilley, the tele- 

 scope maker, of Islington, in 1824 ; it was an uncemented triplet, and 

 cost 90Z. Mr. J. J. Lister, in 1824, began experimenting with achro- 

 matic object-glasses ; on seeing a 4/10 and a 2/10 which Tulley had 

 made for Dr. Goring, he suggested some improvements, the result of 

 which was the production of the celebrated 9/10 by that firm. Sub- 

 sequently Mr. Lister ground and polished leuses himself. On 

 January 21st, 1830, he read his paper on the two aplanatic foci before 

 the Royal Society. In 1837 he designed an 1/8 object-glass for 

 Andrew Ross. This had a triple front (Mr. Listers invention) and two 

 doublets (fig. 117) ; for the lower powers he suggested a double com- 

 bination, which was formed by combining a front (one of Andrew 

 Ross's failures) with one of Lister's backs (this is Lister's own account ; 

 but, according to Ross, it was a Lister front that was combined with a 

 Ross back). I am rather inclined to think that there is a clerical 

 error in Lister's account, and that Ross is correct. If this is so, then 

 the lens will have a back similar to the middle combination of the 

 lens in fig. 117 and a front of the form shown in fig. 121. In 1840 

 Lister obtained Ross's consent to instruct James Smith in the con- 

 struction of object-glasses; he says, "even in 1843 it was with the 

 understanding that he should not go to deeper powers than 1/4 in., 



