minute, which is not capable of being resolved 
into smaller particles, as far as our means of 
observation can carry us; and the absurdity of 
the particular dimensions assumed is further 
shown by the fact, now well known, that there 
are very numerous species, and countless indi- 
viduals, among the Polygastric animalcules, 
whose whole bulk is susie less than that of one 
of the so-called ultimate particles, and which 
contain within this a considerable number of 
different organs. The following statements 
made some years since by Ehrenberg will give 
a very good idea of the mode in which the 
size of such organs and of their component 
parts may be approximately known, when they 
are themselves too minute for measurement. 
“T could plainly distinguish with a micro- 
er magnifying nearly 800 diameters, Mo- 
s, which were filled with colouring nutritive 
substances, and which possessed voluntary mo- 
tions, but the entire and greatest diameter of 
whose body only amounted to the ;,);th or 
spoth of a Parisian line. I could perceive 
in the largest individuals of this form as many 
as six, and in the smallest as many as four, in- 
_ ternal sacs coloured blue by indigo, which at 
_ times did not occupy half the internal dimen- 
sion of the animal. Such a sac, therefore, of 
an animalcule measuring ,A;th of a line, 
_and if we suppose only four sacs occupying the 
half of it, (therefore not one of the smallest,) 
4S qafpth of a line in size. Further, if we 
‘Suppose the single colouring particles, with 
which the stomachs are filled, not to be nume- 
Tous, it would be against all probability not to 
think that they were filled by several particles. 
_ Let us, however, only suppose each sac to 
_be filled with three colouring atoms,—which, 
from the roundness made perceptible by the 
“Motion communicated to them when diffused 
_ through the water, we may well admit,—this 
___ alone affords a proof of the existence of material 
colouring particles of red and dark blue moving 
freely in water, which measure sh,,th of a 
line, or jg3}gth part of an inch in diameter; 
and calculating these objects from the smallest 
__ Of the animalcules, which by actual observation 
were found to be 5th of a line in size, and 
which sometimes contained four coloured points 
in the hinder part of the body, these particles, 
which cannot be distinguished individually by 
By * the eye with a magnifying power of 800, but 
_ which are yet to be recognized as corporeal, 
_ would amount to gj,th of a line, or 
 gmdoth of an inch. Further, the smaller 
_ Monad-stomachs are seen isolated in the body, 
_ and with sharp outlines. In larger Infusoria, 
_ which are th of a line, or more, in diameter, 
___ these internal receptacles are recognized as evi- 
____ dent membranaceous sacs, which often make 
their appearance isolated, when the animalcule 
____ is pressed, or when it divides itself, and which 
¥. have been supposed to be separate infusoria, 
Internal monads. It can be distinctly seen 
that, when two such digestive sacs touch one 
another, the thickness of the partition between 
_ them is, in comparison with the diameter of the 
stomach, extremely small, so that the former is 
Searcely perceptible ; it may be reckoned as at 
MICROSCOPE. 
357 
the most sth of the latter, Granting, how- 
ever, the thickness of the partition to be as much 
as 7th the diameter of the sac, this would 
amount to yedggth of a line, or yahoo th 
of an inch, in monads g¢pth of a line in 
size, in which the stomachs measure but one- 
eighth of the whole length of the body, and 
are therefore jg/5;th of a line in diameter.” 
When similar views are extended to the young 
of the species on which this calculation is 
founded, or to smaller species in the existence 
of which there is good reason to believe, the 
minuteness of structure thus disclosed becomes 
still more wonderful. “ Let not these calcu- 
lations,” it is justly remarked by Ehrenberg, 
“be regarded as playful; they are so far in 
earnest, that they are founded on the contem- 
plation of nature, and are not to be considered 
as a groundless speculation. They plainly de- 
monstrate an unfathomableness of organic life 
in the direction of the smallest conceivable 
space; and if the word infinity be too much for 
what we know at present, let the word unfa- 
thomableness, which I have purposely em- 
ployed, avert from me the reproach of exagge- 
ration, and establish the direction which the 
physical, chemical, and physiological enquiries 
of our days, should they be rendered fruitful by 
new powers, have to take, and what deviations 
they have to avoid.” 
To these enquiries Ehrenberg has subjoined 
an attempt to calculate the power of vision for 
the human eye, and the ultimate power of the 
microscope. From his experiments on_ the 
smallest square magnitudes which are ordina- 
rily visible at any distance by the human eye, 
he finds that they vary in different cases from 
yth to yi,th of a line ; but when strongly il- 
luminated, much smaller bodies can be seen, 
metallic particles of y4th of an inch being 
visible in common daylight; and non-transpa- 
rent threads of 4),th of a line in thickness 
being distinguished, when held between the 
eye and the light. Hence the size of the mi- 
nutest objects visible with a given magnifying 
power of the microscope might be determined 
by dividing their apparent dimensions, as just 
stated, by the magnifying power; thus no 
square corpuscles of less dimension than 
sayoth or 4dath of a line could be seen with 
a magnifying power of 100 diameters. In 
practice, however, owing to the degree of im- 
sedate which must necessarily attend the 
est-constructed instruments, the minuteness of 
the smallest visible objects cannot be judged of 
entirely by this rule; since, in order that it 
should be correct, it is necessary that the 
object of yi,th or s4,th of a line in dia- 
meter, should be represented to the eye as 
clearly by a microscope magnifying 100 dia- 
meters, as a real object of Ath or pth of a 
line would be; this is very far from being the 
case, owing to the loss of light by reflection in 
passing through the lenses, as well as to the 
errors of the lenses themselves, which can never 
be perfectly corrected. With a magnifying 
power of 1000, which is perhaps the highest 
that has yet been employed to real advantage, 
the minutest particle which could possibly be. 
