442 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. [December 2,1871. 
movable lamp is under more perfect control than 
daylight can well be, and is also in this England of 
smoke and cloud more to be relied upon for con¬ 
stancy. Whichever be used, the light should fall 
upon the instrument from the left-hand side, if the 
observer use his right eye chiefly (as most do); and 
from that side in any case, if there be many adjust¬ 
ments to be made of the illuminative apparatus, 
which, being made with the right hand, would cause 
a disagreeable shadow were the light allowed to 
come from that side. By daylight care should be 
taken that the direct rays of the sun are not allowed 
to fall upon the object. Light from a white cloud 
opposite to the sun, or nearly so, is best; that from 
a blue sky is wholly unfitted for micro-polariscope 
work, as it is chiefly composed of light already 
polarized in one plane, and, therefore, only trans¬ 
missible through one direction of the polarizer. 
Lamps. —Their name is legion. We cannot ad¬ 
vertise them all. Personally, we prefer an ordinary 
paraffin lamp, which need not cost more than a 
couple of shillings, or, including Mr. Swift’s Blank- 
ley’s new chimney, about five shillings. Such a 
lamp embodies nearly all the advantages of the 
most elaborate, and is not an addition to the para¬ 
phernalia which so often disturbs the mind of one’s 
better half when his microscopical laboratory hap¬ 
pens also to be liis or her sitting-room. The addition 
to the lamp of a piece of glass stained to a decided 
neutral blue tint is very pleasing, and gives great 
relief to the eye, as most of the yellow rays that are 
so disagreeable and wearying are stopped back. 
But if such be used, it is needful to use a larger 
flame than would be otherwise needful. Gas is, in 
our notion, simply hateful for microscopic purposes, 
on account of its great unsteadiness, heat and its 
products of combustion. 
Seated then at the table, not too high as to neces¬ 
sitate the craning of the neck, nor so low as to 
cause an ugly stoop (upon all these little tilings suc¬ 
cess in microscopy is dependent to a greater extent 
than is commonly recognized by even experienced 
microscopists), with the light of his lamp well ad¬ 
justed, to avoid either smoke or glare, and the lamp 
a little to his left, the tyro may begin to work. 
He cannot do better than familiarize himself with 
the varied effects produced upon some homely ob¬ 
ject, such as a section of wood, by direct and oblique 
light falling at different angles. In other words, 
he should begin by learning the use of the mirror, 
used with those objects which are sufficiently 
transparent to allow light to pass through them, 
and the bull’s-ejm condensing lens, used to throw 
light upon those objects that are too thick or other¬ 
wise too opaque to be viewed as “ transparents.” 
One of the earliest lessons we hope he will learn will 
be that too much light renders it difficult or impos¬ 
sible to see the details of an object, especially if low 
powers be used. From this he will learn to alter 
the focal adjustment of the mirror or condenser, by 
moving it nearer to or further from the object under 
view, and also that the intelligent use of the several 
apertures in the diaphragm plate will greatly aid 
him in his efforts to obtain just so much hglit, and 
no more, than is necessary. Collins’ iris diaphragm, 
if he be so happy as to possess it, will place lite¬ 
rally, as well as figuratively, at his finger-ends, 
through a few turns of a milled head, the means of 
doing this to the greatest possible nicety. Having 
become thus far conversant with the “ go ” of the 
microscope, our friend may safely begin to think of 
entering upon that particular department of micro¬ 
scopic work into which choice, or the fates, may 
happen to call him. That is to say, having become 
master, to some extent, of the instrument, he may 
proceed to learn how to prepare objects and fit them 
for observation. Here, however, we cannot at this 
moment attempt to help him, as we want to say a 
few words to him and to more advanced micro¬ 
scopists respecting their part of microscopic work. 
There is, perhaps, no branch of science in which 
what astronomers call “ personal errors ” more 
abound, or where the poet’s aphorism, “ tilings are 
not what they seem,” is more applicable. A few of 
these “ errors of interpretation ” may be briefly 
noticed. 
1. Foreign matter. —The presence of foreign mat¬ 
ter in the preparations of young, and especially care¬ 
less microscopists, is the source of great perplexity, 
and the fruitful cause of wrong conclusions. Per¬ 
haps the most frequent of these are air bubbles. All 
beginners in microscopy are perplexed with these; 
the more so as they are often the most prominent 
features in even good slides by very experienced 
men. Usually a very little experience will enable 
the observer to decide as to the nature of the queer¬ 
looking black rings with bright centres that he sees 
in the field; but there are cases where,—the bubbles 
being exceedingly minute and confined within a deli¬ 
cate tissue, which alters their shape, and conse¬ 
quently their refractive power,—it becomes somewhat 
difficult to decide upon their nature. It is, under 
these circumstances, a matter of great care and skill 
to decide whether the appearance is due to the pre¬ 
sence of air, of oil, or, in some cases, of water. The 
question, if solved at all, will be solved by careful 
observation of the effect produced by alteration of 
focus. The milled head of the slow movement must 
be turned very slowly until the objective is raised 
out of focus, and then reversed until it has been de¬ 
pressed out of focus. Oil globules become lighter , 
as the objective is raised, and darker as it is de¬ 
pressed, whilst water globules and air-bubbles, sur¬ 
rounded by oil or balsam, do exactly the reverse. 
The explanation is, of course, to be found in the 
very different refractive powers of the three sub¬ 
stances. In the case of the oil globule in water, 
the globule acts as a convex lense of short focus, the 
other globules acting as concave lenses. In the ex¬ 
amination of vegetable and pathological prepara¬ 
tions, it is often of essential importance that the 
observer should be able to detect the difference 
between a vacuole, an air-bubble, fat or resin glo¬ 
bule ; and no pains spent in becoming familiar with 
their several appearances will be regretted. Par¬ 
ticles of “ dust ” are also the source of frequent error, 
and we would strongly urge the student to acquaint 
himself with the microscopical appearance of such 
substances as compose the ordinary “dust and flue” 
of his rooms. The nature of this pest to housewives 
varies so much in different localities that we cannot 
particularize all its ingredients. The following are 
the most perplexing:—butterfly scales, starch gra¬ 
nules, portions of wood fibres, hairs, cotton and 
wool fibres, leaves, fungi spores, and, by no means 
least, excessively minute particles of soot and other 
mineral matter. Nothing but experience will serve 
the student here, and fortunately it is easily and 
inexpensively gained. 
{To he continued.) 
