NOTES AND MEMORANDA. 
47 
lent results. Further experiments have led to the employment of the 
two amplifiers I now describe. Either of them is used in a sliding 
tube between the eye-piece and objective, and the proper position is 
found by trial. The first consists of a cylindrical lens, conical in 
shape, with the smaller end concave, toward the object-glass, and the 
larger end convex. This gives a large increase of magnifying power 
and excellent definition when used with the strongest eye-piece of Gund- 
lach, or other makers. The second form is better still, and consists 
of a double concave lens, having a virtual focus of about IJ- inch, at 
the end of a tube about 6 inches long, at the other end of which is the 
ordinary negative eye-piece. In both these forms the extent and 
flatness of the field is quite remarkable, as well as the amount of light, 
while the amplification is very great. With a periscopic eye-piece of 
Gundlach, or the No. 3 of the same maker, or with the strongest eye- 
piece of Crouch, my ^th objective defines the semi-lenses on the 
frustule of Pleurosigma angulatum, the markings on S. gemma, or 
Grammatophora suhtilissima, with a power of 4000 diameters." 
The Microscopes in the Loan Collection at South Kensington.— 
We are sorry to confess our disappointment with this exhibition, but 
we are bound to confess that it has disappointed us ; firstly, because 
the collection of instruments is so meagre — the Eoyal Microscopical 
Society being alone well represented ; secondly, because it is badly 
arranged ; and thirdly, because there is an utter absence, save in one 
or two instances, of explanatory cards attached to the instruments. 
We had hoped that the subject which of all others has created most 
discussion in the microscopical world — the immersion system — would 
have received particular attention ; but we have not found that any 
attempt has been made to illustrate it. Then there is an utter absence 
of that chronological succession which would have been useful to the 
ordinary student as well as to the histologist. Indeed, almost the 
only novelties that we have observed are the moist chamber recently 
described before the Royal Microscopical Society by Messrs. Dallinger 
and Drysdale, and the contrivance exhibited by Professor Klebs for 
studying the multiplication of the ScMzomycetes. Of the earlier instru- 
ments are those — some of which are familiar enough — of Martin, 
Janssen, Lyonet, and others. An instrument from the Geneva 
Association is also of interest, from the manner in which the object- 
glasses are attached, the arrangement being one of spring-catches, 
which admits of the objective being removed and replaced with con- 
siderable rapidity. We doubt, however, whether the centering of 
such glasses would be at all perfect. 
Of the instruments exhibited, the following are among tbe more 
worthy of notice. A solar microscope, from the Essex Museum; 
Goring's aplanatic engiscope; an interesting case of Lieberkiihn's 
preparations, lent by the Royal Museum of Cassel ; instruments by 
Culpepper, Amici, and Marshal. Dr. Royston-Pigott exhibits two very 
interesting instruments, which we wish had been better placed ; one 
is his kratometer for finding the magnifying power of objectives, and 
the other his microscopic refractometer for ascertaining the refractive 
indices of plates of glass. Among M. Nachet's exhibits may be 
VOL. XVI. E 
