106 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Mr. Chadwick’s paper on Leack’s Lantern Microscope, reported in the 
issue of Nov. 13th. 
In the first place, Mr. Chadwick is dead against every authority 
regarding magnification. Extreme magnification, such as Mr. Chadwick 
suggests, is condemned by every authority of note, both for the Micro- 
scope and for the lantern Microscope. That the magnification which 
enables the observer to see all the details of an object is the largest to 
which it should be subjected, anything beyond this defeating the pur- 
pose. Mr. Chadwick says that, with his arrangement, high powers can 
be used for class and other demonstrations, although he has previously 
stated that the arrangement of condensers is only adapted for objectives of 
4/10 in., which is by no means a high power. Mr. Chadwick cannot 
surely be ignorant of the fact that lantern Microscopes, of whatever 
make, have long been discarded by college authorities where high powers 
are required. I see, too, that he has come round to my views, and 
does not recommend the use of special objectives. 
His last paragraph but two is a contradiction of the previous 
portion of his paper, where he leads us to suppose that he can use 
high powers — that is, of course, 1/15 in. or 1/20 in. objectives — with his 
arrangement, simply because he uses an alum-trough. What he says 
is simply this : in order to use a high power requiring a large amount 
of light, interpose an alum-trough which stops 50 per cent of the light. 
Mr. Chadwick does not seem to be aware of the fact that it is possible 
to focus the heat-rays at a point beyond the luminous rays, and thus 
avoid all heating of the slide. I should just like to inform Mr. 
Chadwick that the substage condenser of which he speaks, and the 
novel way of interchanging the objectives was used by me more than 
sixteen years ago, and shown to Mr. Leach in 1876. 
In conclusion, Mr. Chadwick says that lantern Microscopes which 
have no alum-trough are self-condemned. This I deny, as I do not 
use an alum-trough and never will, and I may say that I have never 
melted a slide.— J. A. Furnivel.” 
“ I am pleased to see Mr. Furnivel’s plain and simple defence of 
himself on this subject. He may fairly be considered the father of the 
simple lantern Microscope, and as I have worked with both bis simple 
form, without alum-trough and also with Leach’s, I may say that 
experience fully bears out his statements. That it is possible with 
either form to get a large projection on the screen with a good lime- 
light is no doubt correct ; but after a most careful testing of both 
under precisely the same conditions, I most certainly prefer Furnivel’s 
at less than half the price. My object in testing both was to obtain 
a clear definition of the different yeast-cells on the screen, but after 
repeated trials, with the assistance of some experts with the lantern 
and Microscope, we failed totally with both, the best results being 
obtained with Furnivel’s arrangement. With a Powell and Lealand 
1/4 in. apochromatic the results under the best conditions were most 
unsatisfactory, and we found with either form the highest power which 
could be used was a 4/10. 
It sounds very large indeed to talk about the proboscis of a blow-fly 
16 ft. long; but the fact i6 that the same would be far better shown if 
only 3 ft., and would make a much more effective picture in any ordinary 
