582 EHRENBERG ON THE POWER OF VISION OF THE EYE, 
Mechanists and less experienced observers are very often in error 
about this, and imagine that by clearness of the small magnifying pow- 
ers they compensate for the strongest. Since, according to the state- 
ment of Herschel, Amici’s microscope magnifies with clearness 3000 
times, it should be the endeavour of opticians not only to imitate the 
form and method of this instrument, but more especially to multiply 
and simplify in every possible way that property of the highest distinct 
achromatic magnifying power. For the general study of the finer or- 
ganization of all organized beings it is needful to possess in our days a 
clear achromatic magnifying power of at least 300 to 400 times in dia- 
meter. Microscopes which are of less magnifying power are, notwith- 
standing all art, beauty and clearness, not to be recommended to stu- 
dents and public establishments. Costly screw micrometers, more than 
three or four achromatic object glasses, which may be used single or 
together, reverberatory apparatus, and glass prisms, are mostly unneces- 
sary, and of advantage but rarely and in limited cases; and their use 
not proportionate to their cost. On the contrary, there are various 
things, especially a fine glass micrometer, and separate powerful mag- 
nifying eye-glasses, and double mirror, which really help and supply the 
wants of the active and careful observer. 
I cannot promise myself much from the solar microscopes until they 
are further mechanically developed. Those which I have had the op- 
portunity of seeing may certainly be considerably improved, and their 
‘power increased. I conclude by again repeating the observation, that 
there are, putting aside all inorganic bodies, even in the kingdom of or- 
ganic bodies whose constituent parts or molecules are generally con- 
sidered to be the coarsest, magnitudes capable of direct proof which 
are in diameter zg45, Of a line ; and others that can be proved indirectly 
which may be less than a six millionth part of a Parisian line in diame- 
ter; that the ideas often expressed respecting atoms, as subjects of 
experience, are somewhat tvo confident ; finally, that the power of 
the microscopes which we at present possess does not in its maximum 
amount to more than to make distinctly visible long opake threads of 
panaen diameter, and square superficies or globules of ;;;> of a line 
in diameter ; and that for these latter they must be increased forty 
times in order to satisfy what is required for reaching directly those mi- 
nutest parts of organic bodies whose existence has been inferred from 
simple deductions; and that we are not to entertain a thought of per- 
ceptible or ever attainable simple matter, or material primitive con- 
stituent particles. 
ADDENDA. 
1. As regards the Spermatazoa, which might be regarded by many 
persons as very important in the decision of the question of the 
& ssl hipadis ees 
