PROCEEDINGS OF SOCIETIES. 
281 
the objective. This adjustment of position was best accomplished by 
having the amplifier screwed to the end of a tube arranged with rack- 
work in such a manner as to traverse six or eight inches, because we 
could thus compensate for a want of complete correction in the objec- 
tives employed. 
The advantages obtained by using an amplifier were, in the first 
place, gain in magnifying power, as could be seen in his microscope 
upon the table, when, with an amplification of only 800 diameters, 
afforded by a four-tenth of an inch objective, he had on exhibition the 
Navicula angulatum resolved into dots all over the field, which was 
apparently more than sixteen inches across. By the aid of an amplifier 
we also gain a greater focal distance, and an increase of flatness of 
field. 
Amplifiers have been employed in telescopes for the past fifty 
years, but ten or twelve years ago they were only adapted to micro- 
scopes, in this city at least, by one or two amateurs. Subsequently, 
Mr. Tolles, of Boston, saw them in use here, and on his return home 
made one, apparently with gratifying success, as he has since kept 
them in stock. Some few years since, Mr. Dickinson, of New York, 
wrote a paper upon amplifiers, claiming that by their aid. he could 
obtain a power of 100,000 diameters ; but objects thus magnified are 
visible only as dim shadows, similar to those shown by the solar 
microscope, quite unfit for data in scientific work. Such amplification, 
however, may be employed upon diatoms, the resolution of which does 
not require definition. 
Dr. J. G. Eichardson inquired of Dr. Hunt whether, in his 
opinion, the y%th objective associated with his amplifier, as he had it 
upon the table, and eye-pieced so as to give a power of 800 diameters, 
was equal to his Powell and Lealand's yV^h immersion lens, combined 
with the A eye-piece. 
Dr. Hunt replied that on histological work the results were not 
quite so good, but on Pleurosigma angulatum he considered them 
fully equal. The combination of amplifier and objective which he 
used was, however, a merely accidental one, so that a skilful optician 
would probably be able to arrange the lenses more efficiently, and 
thereby enable microscopists to obtain this greater amplification at a 
much lower cost, and yet with definition good enough for scientific 
work. Dr. Pigott's aplanatic searcher appeared to be a modification 
of the amplifier, but had proved so unsatisfactory in his hands that 
he had entirely laid it aside. 
Dr. Hunt also exhibited a beautiful specimen of the Protococcus 
nivalis, or red snow, which he believed had been discovered for the 
first time within the United States, by Mr. Harkness, of California, 
who found it growing upon the Sierra Nevada mountains. For a long 
time it was a matter of dispute whether this organism belonged to the 
animal or the vegetable kingdom ; but from observations made upon 
specimens brought from the polar regions by Captain Parry in 1815, 
and which grew in bottles of snow, its vegetable nature had been 
demonstrated. In the growing stage this plant is of a green colour, 
and it is only the resting spores which present the brilliant red hue 
