SUMMARY OP CURRENT RESEARCHES RELATING TO 
126 
The construction of this formula is very simple. From the points 
q and q x let two normals be drawn to the axis ; through the centre c 
draw c t x until it meets in t x the normal passing through q 1 ; let c x t be 
drawn through the centre c x parallel to it, until it meets in t , the other 
normal q t. Having then joined the principal focus p (which we suppose 
to be known) with t, let a parallel to p t be drawn through t x ; the point 
p x , where it cuts the axis, will be the other focus, or the principal 
distance of the lens. 
The same graphic process, and therefore the formulas derived from 
it, are very easily applied also to optic systems composed of lenses 
without thickness. In this case we first determine the successive images 
of the centre of the first and of the last lens seen through all the others ; 
then, considering the centres of the lenses as we just before considered 
the centres of curvature (since we suppose the rays to pass through 
these centres without deviation and without displacement) we make 
relatively to them and to their images the constructions already indi- 
cated, and so we solve with rapidity all problems relating to optic 
instruments composed of thin lenses.” 
(6) Miscellaneous. 
“New Inventions.” — “Her Majesty’s Royal Letters Patent have been 
granted to the inventor of a wonderful as well as useful little appliance. 
This is a Pocket Microscope and Floriscope combined, about 3 in. in 
length and 1J in. square. It is constructed upon an entirely new 
principle, and has a magnifying power and definement superior to some 
of the most elaborate and expensive instruments, and yet so simple that 
any schoolboy or girl can use it. Its magnifying power is registered as 
150 diameters, or 22,500 surfaces, and distinctly shows all the thou- 
sands of different kinds of animalcula in water, &c., or any other micro- 
scopic objects. This new patent was sealed by the Comptroller-General 
of Patents on the 13th of August last, and is now offered to the public 
at the nominal price of Is. each, and sent free by parcel post upon receipt 
of postal order value Is. — stamps not taken — with a 12-page pamphlet 
of instructions for use, and a large double sheet of engravings in black 
and gold (with key) free. The inventors and manufacturers also 
guarantee that, in any case where the instrument is not approved of 
and returned within reasonable time, a postal order value Is. will be 
forwarded by return of post. The medical profession, chemists, school- 
masters, teachers and students, as well as parents and guardians, should 
send for one on approval. This is no foreign rubbish, but of good 
English workmanship throughout. Address, Conway Rae & Company, 
The Premier Patent Microscope Depot, Stafford Street, Birmingham.” 
Upon reading the above advertisement in ‘ Nature’ * we applied for 
one of the Microscopes, and were informed that for an additional remit- 
tance of 6 d. we should receive an instrument of superior make, giving 
“ better definement,” with four extra “ object-glasses,” and a larger 
pamphlet of instructions. As we were desirous of comparing the two 
qualities of Microscopes, we requested both to be forwarded. 
The lower priced one consists of a tin tube of square section, having 
a tin diaphragm with square aperture in the middle. At one end is 
* October 11th, 1890. 
