during the past twenty years with these 
glasses would fill volumes. 
Such glasses are not too insignificant 
to be called microscopes, even though 
their limit of power is so small. Their 
limitations, however, eucourage the ad- 
vance to the compound instruments such 
as are exhibited here this evening, aud 
which range in value from twenty-five 
dollars to many hundreds) My reasoa 
for mentioning values is that many have 
an idea that what seems like a great in- 
strument is necessary for microscopic 
research and their inclination is thus 
restrained by the apparent complexity 
and cost. Not only is such a view iucor- 
rect but it is even unwise that miicro- 
scropic work should begin with coniplex 
avd high-powered instruments. There 
are so many thivgs to observe that a 
simple cheap instrument can afford 
instruction and amusement for a long 
time and it is only after experience has 
been gained that it is desirable to go fur- 
ther into this branch of science, which is 
so inexhaustible as to be a pever-enling 
source of pleasure. 
We all know that study is pursued for 
two purposes; the acquirement of facts and 
the training of the mind. The use of the 
microscope is an unusually pleasant com- 
bination of the many factors in education, 
for by it facts are acquired in a pieasure 
able mauner, while the training is ol a 
kind not common to vther study because 
it gives a field of vision beyond that for 
which nature fitted the eye. 
The earliest reference to the use of 
lenses for the purpose of magnifying was 
about the year 1300 A. D., though not 
until about 1600 was anything made that 
truly constituted a microsc pe. Le,.d 
highly probable that the combination of 
two or more leuses, forming a compoun 
microscope, was invented by Galileo. 
About 100 years later various forms ap- 
peared and by the beginning of this cen- 
tury, or perhaps 1810 to 1820, comipar- 
atively high-powered apd accurate 
instruments were produced, magnifying 
as high as 1,200 diameters. 
Such instrumeuts were, however, so 
rare that only low powers, magnifying 
6 
perhaps a few hundred diameters, were 
accessible to such scientists as used them 
for practical investigation. 
Since that time refinements have been 
slowiy added until now almost any desir- 
able perfection is obtainabie. The per- 
fection which has been reached in 
optical instruments is scarcely known 
even to those who use them aud it 1s only 
those interested in the mathematics of 
the optical qualities who truly appreciate 
the refinemeut which skill has attained. 
The buman eye is usually referred to 
as a type of optical perfection, but even as 
long ago as the last ceutury the grinding 
of lenses had reached such a stage that a 
prominentastronomer remarked that were 
the maker to send him a Jens which had 
as many imperfections as the human eye 
he would return it as detective. 
It would be out of ptace here to under- 
take a description of the instrument, but 
it may be of interest to remark that the 
three prime requirements are inagnifica- 
tion, definition and absence of color. 
The magnifying power is uf course pro- 
duced by the abiiity of the leus to make 
au enlarged image of the object, but if 
in this enlargement the image is distorted 
the definition is impaired. The lens 
must therefore make a true and clear 
image as well as to magnify it. “Dine 
magnification being produced by refrac- 
tion of light is liable to give rise to baads 
of color such as ove as sees through a 
prism acd therefore corrections must be 
introduced iu the lenses to counteract his 
tendency; otherwise the image will be 
blurred by fringes of color aloug the edges 
of all parts of the object. The combina- 
tions of lenses which thus prevent the 
appearance of colors which are not 
natural to the obj-ct are known as achro- 
matic, meaning without color 
Without evtering upon technicalities 
regarding magnification it may be roughly 
said that a small microscope, like a hand 
zlass, magnifies the image once and the 
degree of magnificatiou may range from 
5 to perhaps 30 diameters, according to 
the strength of the glass, while the com- 
pouud microscope inagnifies twice; that 
is, the image is first magnified by tne ob- 
jective lens and this magnified image is 
again tuagnified by the eye piece, It wiil 
therefore be easily seeu that if the objec- 
tive magnifies ro diameters and this en- 
larged image is enlarged ko diameters by 
the eye piece the object will appear to the 
eye maguified 100 diameters. 
In compound microscopes, such as you 
will have an opportuuity to see this even- 
ing, the low powers may range from 50 to 
100 diameters; tre moderate powers from 
roo to 500 and the bigh powers from 500 
to 2,000, with exceptional lenses, which 
eo 
