CORRESPONDENCE. 
225 
Note by Mr. Wenham.. 
Though I have received an intimation from the Editor that the 
discussion concerning the aperture of Mr. Tolles' " 180° " |^th is 
closed, I have asked for the insertion of the above that he may not 
complain of injustice, that the last item of his defence has been sup- 
pressed. What is the character of that defence ? The science of the 
question having been exhausted, it has degenerated into a search for 
inconsistencies in my writings, with the view of imputing to me false 
statements concerning things measured and observed. Had Mr. Tolles 
quoted a few more lines to the end of my sentence, I there stated that 
the aperture was found to he the same if parallel plates were inter- 
posed. I have a vivid recollection of selecting a thickness of glass 
that the lens would just focus through. I now take from my note- 
book as follows : " Maximum distance of dry focus • 013. Will pene- 
trate a cover '018 thick (at adjustment on its under surface)." With 
the slit in focus in each case this plate did not increase the aperture. 
I decline to argue on a principle so obvious as this. The date in my 
note-book is January 17, 1874. So for near fifteen months argument 
concerning this ^th has dragged out its weary length, by Mr. Tolles 
requiring me to answer his " challenges " in defence of the wonderful 
apertures engraved thereon. I can testify that Mr. Tolles commands 
a high degree of manipulative skill, and deserves every success in a 
somewhat hard and profitless line, for his industry and persevering 
experiments for improving object-glasses ; and the tone of his letters 
when left to his own diction speaks favourably for his good nature. 
[The controversy as to Mr. Tolles' ^th objective must now end. — 
Ed. ' M. M. J.'] 
Urinary Deposits — A Note by Dr. Ord. 
To the Editor of the ^Monthly Microscopical Journal.^ 
March 9, 1875. 
Dear Sir, — In referring to some papers by Dr. Bence Jones 
relating to urinary deposits, I find that beyond recording the influence 
of chloride of sodium in modifying the form and increasing the solu- 
bility of urate of ammonia, he, in a paper contributed to the Medico- 
Chirurgical Transactions in 1844, relates experiments which agree 
with and therefore anticipate some of the experiments related in my 
paper read before the Eoyal Microscopical Society in January last. 
At page 111, he records that he heated needles of urates of 
ammonia for some hours at about 212°, so that decomposition took 
place ; boiling water was then poured on and filtered whilst hot. A 
deposit obtained at the end of forty-eight hours consisted of globules, 
and globules with projecting angular crystals and crystals of uric 
acid. This experiment is very like my second experiment with m^ate 
of ammonia in principle and in results ; though Dr. Bence Jones used 
the experiment for a different object from mine. 
At page 113 he writes: "A large excess of needles was boiled 
