the available power of microscopic object glasses, as it appears 
impossible to separate or define lines more numerous than 
ninety thousand in an inch, on account either of the decom- 
position of light or some other cause. It therefore seems 
beyond our power ever to discover more of the ultimate 
composition of matter by aid of the microscope, even were we 
not prevented by the material composition of our lenses and 
organs of vision. 
We have, however, penetrated to the very confines of 
organic life, if not beyond, inasmuch as no organisms appear 
to exist smaller than those we can already see. 
It is, moreover, a curious fact that the smaller creatures 
are composed of fewer elements than the larger ones, and 
that the number of elementary bodies composing them de- 
crease in number as the organisms themselves decrease in 
size. It becomes therefore a matter for speculation whether 
the reason of this may not be, that the ultimate atoms of 
some elementary bodies are larger than others, and that 
these, from their size, cannot be used in the composition of 
the more minute forms of organic bodies, and that smaller 
organisms than those about Tr&oo-th of an inch do not exist, 
because the ultimate atoms of all solid bodies are too large 
to be economically used in their formation. The telescope 
appeared to have infinite fields of distance to explore, but it 
would seem the microscope had nearly reached the limits of 
its possible power. 
Mr. J. B. Dancer, F.R.A.S., then read a paper “On a 
contrivance for regulating the amount of light transmitted 
from the source of illumination to the mirror of the micro- 
scope.” 
