152 
Transactions of the 
TMonthly Microscopical 
L Journal, March 1, 1869. 
Last year T made some observations on immersion lenses ; and 
I am again induced to recommend that they should receive due 
attention, and that their capacities should he fully investigated. 
Mr. Mayall read before us a paper in v^hich he commended those 
of Mr. Hartnack. I believe the only English makers who have 
made lenses of this description for sale are Messrs. Powell and 
Lealand, and I learn from Mr. Lobb that they work advantageously 
on difficult lined objects, but he does not give them a preference for 
ordinary research. A valuable paper, accompanied with photographs 
of Nobert's test-lines referring to these and other lenses, was com- 
municated to the Society by Assistant-Surgeon and Brevet Lieut.- 
Colonel Woodward, of the United States army. This paper was 
printed in the ' Quarterly Journal of Microscopical Science ' for 
October, without any acknowledgment of its having been sent for 
publication by this Society. Mr. Woodward states that out of the 
series of lenses at his disposal, including an ^th. of Koss, made two 
years ago, a tV^^ of ToUes, made five years ago, an immersion 
system, No. 11, by Hartnack, made two years ago, an |th, an 
immersion tV^^j ^ Tr^ti/ by Wales, &c., he obtained the best 
results with the -^^th and ^^-Qth of Powell and Lealand. The low 
prices of these immersion lenses as made by Hartnack and Merz 
must be considered as well as any merits they may be found to 
possess ; and our English opticians will have to pay more atten- 
tion than they have hitherto done to the question of price. 
I hope the immersion lenses will be fairly studied, not only 
upon difficult diatoms and Nobert's test-lines, but upon objects 
requiring penetration and other qualities which lined objects do 
not sufficiently test. It is well known that many of the most 
important discoveries have been made and are made with objectives 
of moderate and even small angles of aperture ; and we shall go 
backwards instead of forwards if we forget this fact, and estimate 
our glasses too exclusively by the difficulty of the lines they can 
resolve. 
In reference to this subject I will only add that Messrs. Powell 
and Lealand make their immersion lenses with removable fronts, so 
that they maybe used when required upon the non-immersion plan. 
During the past year no very striking instrumental novelties 
have been presented to our notice. Mr. Hall brought before us an 
achromatic condenser in a modified form, and with many appliances ; 
and as this instrument was presented to us by Mr. Swift, our FeUows 
can examine it at their leisure. Mr. Lee called our attention to 
improvements made by M. Nachet in his binocular microscope, and 
Mr. Heisch exhibited his modifications of the same instrument, 
which, as you will remember, is capable of producing pseudoscopic 
as well as the stereoscopic effects ; this is accomplished by a simple 
method of changing the direction of the rays so that when the 
