THE YOUNG SCIENTIST. 
Ill 
Grasping the Me.— In using the larger files, 
intended to be operated by both hands, the 
handle should be grasped in such a manner 
that its end will fit into, and bring up against, 
the fleshy part of the palm, below the joint of 
the little finger, with the thumb lying along 
the top of the handle, in the direction of its 
length; the ends of the fingers pointing up- 
wards, or nearly in the direction of the oper- 
ator's face. 
The point of the file should be grasped by 
the thumb and first two fingers, the hand 
being so held as will bring the thumb, as its 
ball presses upon the top of the file, in a line 
with the handle, when heavy strokes are re- 
quired. When a light stroke is wanted, and 
the pressure demanded becomes less, the thumb 
and fingers may change their direction, until 
the thumb lies at a right angle, or nearly so, 
with the length of the file; the positions 
changing more or less, as may fee needed to 
increase the downward pressure. 
In holding the file with one hand, as is often 
necessary in filing light work, pins, etc., the 
handle should be grasped as already described, 
with the exception that the hand should be 
turned a quarter turn, bringing the forefinger 
on top, and lying along the handle nearly in 
the direction of its length. In this position, 
the freest action of the hand and wrist may be 
had upon hght work. 
Amateurs will find that by following these 
directions, the movements of the file will be 
simplified, and made somewhat easier than if 
grasped at random and without consideration. 
Drawing Boards. 
Ed. Young Scientist— 1 have used drawing 
boards for many years ; I used to think they 
must have cleats on the ends or back. When 
strong cleats are put on, as you direct, there is 
little or no advantage in gluing up the board 
from narrow strips; but where the board is 
80 glued up, there is no occasion for any cleats ; 
indeed it is better without them. The cleats 
confine the parts to which they are attached to 
one unvarying width, while the parts between 
the cleats are, in a measure, free to expand and 
contract with alterations of the hyguometric 
conditions to which they are exposed. Conse- 
quently the edges of the board cannot remain 
straight. 
A double elephant board made of -i-inch 
strips, and I4 inches thick, will be abundantly 
strong without cleats; it will not warp enough 
to be troublesome, and the edges will stand 
much better than if made as you direct. It 
has the additional advantages of being cheaper, 
lighter, less bulky, and of having either side 
available. J. B. S. 
BOOK NOTICES. 
A Treatise on Files and Rasps;: Descriptive 
aud Illustrated. For the use of Master Me- 
chanics, Dealers, etc.; in wliicii the kiuds of Files 
iu most commou use, and the newest aud most 
approved special tools connected therewith are 
described, givmg some account of their principal 
uses. With a description of the process of man- 
ufacture and a few hmts on the use aud care of 
the file. Published by the Nicholson File Co., 
Providence, E. I. 
Although intended chiefly as a means for adver- 
tising the files of the Nicholson File Company, this 
handsome quarto volume contains a great deal of 
valuable practical information upon the subject of 
files in general and their use. It is well illustrated, 
and must prove a valuable addition to the library 
of any mechanic. 
Iridescent Glass._Some specimens of ancient 
glass are remarkable for the exquisite iridescence 
which they display, some of them surpassing in 
beauty the colors on the neck of the dove. A recent 
number of "Le Propagateur," in commenting on 
this new iridescent glass, makes the following re- 
marks in regard to its manufacture: " In Germany 
the glass to be iriiized is heated, and a metallic 
oxide deposited on its surface by reduction. The 
oxide forms striae on the surface, and these deter- 
mine the phenomenon of iridescence. Bismuth 
seems to be much used in the principal glass works 
as the iridizing metal. In fact, M. Peligot, the 
eminent chemist, who has analyzed these irides- 
cent glasses, found appreciable quantities of bis- 
muth in them. Any metal whatever might, per- 
haps, produce the same result." 
Indelible Indian Inlc.—Draughtsmen are well 
aware of the fact that lines drawn on paper with 
good India ink which has been well prepared, can 
not be washed out by mere sponging or washing 
with a brush. Now, however, it is proposed to 
take advantage of the fact that glue or gelatine, 
when mixed with bichromate of potassa, and ex- 
posed to the light, becomes insoluble, and thus 
