248 THE NORTHERN MICROSCOPIST. 
bring about a universal guage for eyepieces and stage-fittings, and 
to discourage the purchase of stands with small tubes. Mr. 
Collins’ microscope sells for £5 10s. od., in a mahogany cabinet, 
with a one-inch objective, a quarter-inch and an A eyepiece. 
SHEFFIELD MICROSCOPICAL SociETY.—At a recent meeting of 
the above Society Mr. Ellis gave a very instructive paper on the 
“Human Eye,” in which he described fully the physiological 
structure and names of the different parts of the eye, the diseases 
to which the eye is subject, the causes of such diseases, and the 
remedies by which some are cured. He explained the different 
theories for the means of focussing the eye, so as to see near and 
far off objects; the cause of bad eyesight and the kind of glasses 
to use for the same. Mr. Ellis illustrated his paper by a number 
of drawings and several eyes and portions of eyes. 
A NEw Potarisinc Prism.—Professor S. P. Thompson read a 
paper at the British Association meeting, in which he said that he 
had tried to improve upon Nicoll’s prism by cutting Iceland spar, 
so that the reflecting film has a principal plane of section, and thus 
he obtained a wider angle of aperture, so desirable for microscopic 
work, and abolished the blue band which interferes with the clear- 
ness of the field of vision. 
YELLow FEvER.—M. Pasteur has resolved to visit the Bordeaux 
lazaretto to study yellow fever, and ascertain whether it is due to a 
parasite, and can be guarded against by inoculation. 
. MANCHESTER NATURAL History SociETy.—At a recent meet- 
ing of this Society several interesting communications were made. 
The Chairman (Mr. W. Chaffers) exhibited some micro-photo- 
graphs which had been taken by Mr. Furnival, there being amongst 
them the tongue and eye of a fly, a human artery, showing trans- 
verse and longitudinal sections, and a number of grouped diatoms. 
Mr. Robert Parkes showed, by means of the microscope, a variety 
of beautiful organisms illustrating pond-life, both animal and vege- 
table. Some of the specimens shown were the //umatella repens, 
Vorticella nebulifera, Nitella, and Volvox globator, the latter being 
so abundant as to give a green hue to the water. Mr. Thomas 
Rogers contributed a large grasshopper and two species of Cicads 
from New Orleans, and from the island of St. Thomas a fine speci- 
men of the urchin fish (Déodon hystrix ). 
ORGANISMS OF NirRiFIcATION.—A communication made by 
Mr. Warington to the British Association related to what chemists 
call the origin of nitrification, or the transformation of nitrogenous 
matter, such as sewage and animal matter, into nitrates in the soil. 
The result of Mr. Warington’s investigations is to show that the 
