142 
SHORT NOTES ON PROFESSIONAL SUBJECTS. 
89. Captain J. P. Nolan’s Range-finder. Communicated by the in¬ 
ventor. 
In No. 87 “ Short Notes on Professional Subjects, 5 * published with No. 3, 
Vd. VII. of the “ Proceedings,” is a diagram for finding ranges, by Captain 
Tracey, R.A. In the “Mechanics’ Magazine” of February 24 is a drawing of 
a mechanical calculator for finding ranges, by Lieut. Watkins, R.A. In my posses¬ 
sion is a mechanical calculator for determining ranges, the main portion of which 
closely resembles the other two. 
All these mechanical calculators are rulers containing 
(1) A line of lays proportional to the bases from which the ranges are measured. 
(2) A line of lays proportional to the sines or arcs of small angles. 
(3) A line of lays proportional to the ranges to be determined. 
In addition, my ruler contains artifices for effecting addition and subtraction. 
Except the omission of the artifices for subtraction and addition, the three rulers 
are almost identical in construction, as they are completely the same in design and 
principle. 
The most curious feature of resemblance is that all three contain a superfluous 
line of logarithmic divisions; the base line of lays being wholly unnecessary, as 
the lays of the ranges can be made to serve for the bases as well as for the ranges. 
This line has been accordingly suppressed by me in my later mechanical calculators. 
The resemblance being so very close, I think the dates of the construction of 
the three range rulers should be compared. 
My system was not published until May, 1869 ; but the original range ruler— 
that to which I have referred, and which I still possess—was privately shown by 
me to the Ordnance Select Committee and to some artillery officers in June, 1867. 
