60 THE AMERICAN MONTHLY [Mar 
The second note was a description of the first English 
achromatic objective, made by W. Tulley. It was a trip- 
let and was made at the suggestion of Dr. C. R. Goring, 
who paid $450 for it. The focus of the combination is 
0:933 inch, initial magnifying power 10°72, N. A. -259, and 
the O. I. the large amount of 24:2. Mr. Nelson then 
described the Chevalier-Euler achromatic objectives of, 
1823-’24 and 1824-’25. These were doublets, and in 1827 
Mr. J. J. Lister put one of Chevalier’s doublets as a front 
and a Tulley’s triplet as a back lens. The focus of the 
combination was 0°52 inch: it was the finest microscopic 
objective that had up to the time been produced, and was, 
strictly speaking, the first really successful scientific mi- 
croscopic objective. Lister’s labors in perfecting object- 
ives and the great use they had been to the leading op- 
ticians of the day were referred to. 
The third note was on “A Useful Caliper Gauge.” It 
can be,purchased at any watchmaker’s tool-shop for 75c. 
or $1 and is convenient for measuring the thickness of 
cover-glasses, and for low-power work the scale may be 
placed on the stage of a microscope and the constant of an 
eyepiece micrometer be found by comparison with the mm. 
divisions. The president gave an account of some invest- 
igations which he had made in reference to a disease that 
had caused great mischief in cherry orchards in Kent. 
About fifteen months ago, when his attention was first 
called to it, the disease was prevalent over a considerable 
area, a noticeable feature in connection with it being per- 
sistence in the autumn of the dead leaves on the branches, 
instead of their falling off, as they would have done if the 
trees were healthy. The leaves of affected trees were per- 
vaded by the mycelium of a fungus which destroyed them, 
and as the food of the tree was prepared by the leaves the 
growth of the tree would in consequence be arrested. The 
‘results of experiments in the cultivation of the fungus 
showed it to be one which belonged to the genus Gnomo- 
