564 MICROSCOPY. 
ANGULAR APERTURE OF OBJECTIVES. —Īn communications which 
have appeared in the Narurarisrt and in the ‘ Monthly Microscop- 
ical Journal” of London, different writers have treated of the 
improvements made in the construction of apparatus, and espet- 
ially of objectives, and have chosen their own method of express- 
ing their ideas, and of commenting upon the expressed opinions 
of others; but where the end aimed at is truth, and the result 
sought for is an advance in the quality of appliances, minor 
matters and side issues in the controversies are to be overlooked. 
All lovers of progress in scientific research feel much pleased 
with the labors of investigators who make good use of the exter 
sive means at their control, as well as also with the results which 
have emanated from the patient thought and close study of such 
men as Mr. Wenham and others abroad. We are very apt; 
however, to give too little credit to the intelligent instrament 
maker himself. The mind which combines science with practice 
in its application has great advantages and should be both respected 
and encouraged. 
How we have been forced to modify our opinions, since an angle 
of aperture of, say, 150° in microscopical objectives was consid- 
ered absolutely unattainable! No doubt the very men who — 
and firmly believed those things impossible which are now qui | 
familiar, were as glad as any one, when they became con 
facts, that they had been in error. ; a 
Equally gratified, probably, will be Mr. Wenham, i n + 
shall see for himself that an angle of more than 82 ae : 
attained through balsam. Within a few days, I hari make 
good opportunity to see a qth objective of Mr. Tolles a 
give an angle of 92° through balsam with tank arrang pe 
Mr. Wenham. I feel disposed, however, to let Mr. Toilen k 
of this in his own words, the more so as my time 8 ea ee 
limited. — J. C. 
: a 
recently whee 
Dr. JOSIAH Curtis, Dear Sir:—At my request, you were wont when immersed i? 
measured the angular aperture of an immersion 1-10 in. a, the tank method of 
balsam. You verified the results gained at that time. We use 
Mr. Wenham ( see M. M. Journal, August, 1871). o (upwards): 
The 1-10 in. tested, I stated to you, had iù air angular ap. of 170° (ap ! ui 
In water we found the angle to be 110°-+. Jame, thin, for light, 7 
In balsam the angle was fairly 95°, using petroleum lamp ith "sunlight I got two 
darkened As you will remember I remarked that W . 4d 
s more, others, to hear of res 
t will, I know, be of interest to you, and I am sure to some n bere the angle of aP 
of test of angle in ther cases. Iwill, therefore, set dow 
$ 
