101 
LOGARITHMIC SLIDE dRTJIAES. 
— BY - 
MAJOR S. B. YON DONOP, R.A. 
H AYING, with permission, introduced the use of the Logarithmic 
Slide Rule into the Royal Military Academy and having found 
it extremely useful in solving the many problems connected with the 
study of gunnery, I have thought that, although a number of Artillery 
Officers are already in the habit of regularly using the slide rule, yet 
others may like, perhaps, to have the instrument brought to their 
notice, and may also, after a little practice, find it equally useful. 
The Logarithmic Slide Rule was, I think, first mentioned in the 
Proceedings by Colonel Watkin in a paper published in Yol. XIII., 
No. 13, July, 1885. In 1895, thanks to Major H. P. Hickman, an 
“ automatic plotter ” (invented by that officer) for plotting the 
observations of Siege Artillery fire was brought into the service and 
with this plotter two logarithmic slide rules were used. Since then it 
has been found possible to make the necessary calculations with these 
slide rules and without the “ plotter,” still however working on Major 
Hickman's principle. Thus every officer and many of the non-com¬ 
missioned officers of a siege company must acquire a knowledge of the 
use of the slide rule. Special slide rules are used for calculating the 
perforation of armour and working out automatically other formulae, 
and in the Proceedings of May, 1895, Major Hansard proposed two for 
calculating the battery commander's corrections when conducting 
coast artillery practice. 
The instrument in use at the Royal Military Academy is made by 
Messrs. Davis and Son, Derby, but there are others, both of English 
and French make, very similar in construction. It is a 10-in. rule, 
and it must be remembered that a rule of this size can only be used 
for calculations which do not require more than three figures to be 
accurately found. Longer ones can be obtained if required. 
The slide rule consists of two portions, the “ rule " and the “ slide,” 
and the scales and marks on both sides of these are employed for the 
various calculations. There is also a cursor or sliding frame provided 
with a centre hair line. 
Looking at the front of the slide rule (Fig. 1) will be observed 
logarithmic scales arranged in the following order from the top. 
2. VOL . XXVI. 
