2 
THE YOUNa SCIENTIST. 
his reach, but there is open to him a field 
wide enough and useful enough to employ 
many years, and yield results worth all 
the time and trouble required. 
In the directions which follow we have 
drawn not only from our own experience, 
but from the writings of Brewster, Imison, 
Holtzapffel, Wenham, and others. Modern 
works on optics give no directions about 
the mechanical construction of the dif- 
ferent instruments used, and the student 
who tries to pick up information from 
books will find very little upon the sub- 
ject. ' The older writers gave directions 
which, for the day in which they were 
written, were very complete. We have 
now before us a very elaborate work — 
over two hundred years old — in which the 
grinding of lenses is very fully described 
and illustrated. In this book we find a 
description of a binocular microscope and 
directions for what in modern times is 
known as the local xtGlishing of lenses- 
things which are supposed to be of very 
recent origin. Imison, in his "School of 
Arts," gives some directions for lens- 
making, and Brewster, in his edition of 
Ferguson's "Lectures on Mechanics," 
tells how to grind lenses and specula. 
The most complete treatise on the sub- 
ject, however, is that of Holtzapfi'el, who, 
in the third volume of his "Mechanical 
Manipulation," gives a very full account 
of the grinding of glass for optical pur- 
Xwses, but the optical part of the subject 
he does not touch upon. The most pre- 
cise directions for making objectives, 
prisms, etc., have been given by Mr. 
"Wenham in the Monthly Microscopical 
Journal. Like all the writings of this 
gentleman they are thoroughly accurate, 
minute, and practical. They have re- 
cently been republished by Dr. Beale in 
his book, "How to Work With the Mi- 
croscope," and we propose to embody 
almost the entire matter of these papers, 
with the illustrations, in the articles 
which we shall give to our readers. In 
the chapter given by Beale on this subject, 
there are a number of valuable suggestions 
and additions by Mr. Swift, the well-known 
microscope maker. 
Mr. Eoss, who contributed the famous 
article on the microscpe to the Pouiy 
Cyclopcedia, aiso gave some instructions 
for preparing polishing powders*, for pro- 
ducing flat surfaces in glass, and for set- 
ting lenses. " Eee's Cyclopedia" also 
contains some practical matter scattered 
through different articles. Outside these 
works we know of nothing that is avail- 
able to the young student. 
We have thought it well to point out 
these sources of information so that our 
readers may have an idea of how little 
there is to be found on the subject. 
Ordinary books on chemical and physical 
manipulation (such as Faraday's and 
Williams' works on " Chemical Manipula- 
tion," and Frick's " Physical Technics ") 
do not touch upon the subject of glass 
grinding at all. 
One question which will probably occur 
to the minds of our readers we may as 
well ans wer here. It is this : How much 
optical knowledge must the student have 
in order to succeed ? 
Of course the more the better, but at the 
same time it must be acknowledged that 
but a very slight acquaintance with the 
laws of optics is necessary to enable one 
to make even a tolerably good objective, 
and to use it with good effect. The reader 
who will master the ordinary chapters on 
optics in our school philosophies will be 
able to follow out the practical parts of 
these articles to good advantage. Par- 
ticularly should he study the course of 
light through ordinary lenses, and the 
way in which these lenses form images 
greater or less than the object which 
makes the image. He should become 
familiar with the forms and names of the 
different kinds of lenses, as plano-convex, 
double convex, meniscus, etc., and he 
should inform himself in regard to the 
elementary facts and laws which govern 
the decomposition of light by the prism. 
This much is easily learned, and .may be 
found in any text-book on Natural Phil- 
osophy. Those who desire a popular and 
yet thoroughly accurate book on the sub- 
ject, would do well to study that part of 
Deschanel's Philosophy that is devoted to 
*The directions fjiven by Mr. Andrew Boss, 
Lord Ross, Holtzapffel, and others, for preparing 
polishintr powders, are published in full in the 
" Workshop Companion." 
