SCIENCE 
IS 
KNOWLEDGE. 
KNOWLEDGE 
IS 
POWER. 
A Popular Record of Scientific Experiments, Inventions and Progress 
Copyright Secured, 1877. 
Vol. I. 
NEW YORK, MARCH, 1878. 
No. 
How to Read a Drawing. 
' LMOST every 
reader of this 
journal will, at 
some time or 
[ other, have oc- 
casion to con- 
struct some ma- 
chine or piece of 
apparatus from 
drawings, and it 
will at least be 
necessary for him 
to know how to 
read a drawing, even if he should not be 
able to make one. We propose to give just 
such information as will enable our readers 
to make practical use of any working draw- 
ing that may be placed before them. 
Drawings are of several kinds, such as 
perspective, isometric, orthographic, etc. 
It will suffice here if we call attention to the 
difference between perspective and working 
drawings. Perspective drawings are sim- 
ilar to the engravings usually given m 
books. Thus, the boat, on page 15 of the 
previous issue of this journal is in perspec- 
tive. As a very simple example of such a 
drawing, and of its advantages and defects, 
let us take two blocks of wood placed one 
on the other, as shown in Fig. 1. The pre- 
cise arrangement of the two blocks, and the 
Fig. 1. 
general appearance which they present are 
very well shown, but it would be impossible 
for one not thoroughly versed in drawing to 
ascertain the exact size or proportion of the 
different parts. Measured by the dividers, 
the further ends of the blocks are narrower 
than those that are nearer, and unless the 
reader is able to lay out the lines according 
to which the drawing was made, it will be 
