June 5, 1902] 
NATURE 
139 
workers, foundry-men, &c., 129. Of these men, 832 in number, 
including only those actually at work in the shops, 58, or 7 per 
cent., are foremen, and 178, or 27 per cent., are youths under 
eighteen. Turning now to Leitz, in Wetzlar, who, I may say, 
manufactures microscopes almost exclusively, we find the same 
steady progress, if not exhibited in such a striking degree. The 
numbers employed were : in 1879, 35; in 1884, 100 ; in 1889, 
160 ; in 1894, 200; and at the present day (1899) 253. This 
number is divided up as follows: theoretical staff, 4; office 
and dispatch, 9; mechanics, 164; opticians, 60 ; case work, 
&c., 16. The foremen number 10, or 4°2 per cent., and the 
boys 18, or 7°25 per cent. of the total number actually employed 
in the shops, viz., 240. The firm of Reichert, in Vienna, 
although smaller, shows an almost identical rate of progress 
with that of Leitz, the numbers being: employed in 1879, 20; 
in 1884, 40; in 1889, 75; in 1894, 100; present day (1899), 
150 ; of these, 3 form the theoretical staff, 8 are employed in 
the office and dispatch department ; while of the remainder 120 
are mechanics, 30 opticians and 8 case-makers, &e., the boys 
being 15 percent. of the whole. 
in detail do not always agree with the totals, but I give them as 
TECELVEC. Getaie: (= 
In the most successful of these firms, that of Zeiss, it 
will be noticed what a large percentage (27 per cent.) of boys 
is employed in comparison with the other two—Reichert 
15 per cent., Leitz 7} percent. It will also be noticed that 
the percentage (7 per cent.) of foremen is proportionately high. 
Herein, to my mind, lies the superiority of the firm of Zeiss 
over competitors of their own nationality, and much more so 
over us. I do not wish you to understand that I consider the 
number of boys employed bya firm an unfailing criterion of 
efficiency and progress ; stated in this bald way the proposition 
is absurd, but, when we take this fact in conjunction with the 
well-known excellence of the productions of Zeiss (instruments 
than which no more delicate or difficult of manufacture can be 
found in the whole range of optics), when, I say, we take these 
two facts in conjunction, what is to be said of the organisation 
and system which allows of their coexistence ? I think, therefore, 
that I may be allowed to say that the number of boys employed 
by Zeiss demonstrates their superiority, and not only that, but 
that it gives them a ofen/éal or /atent power of progress, if I 
may use the expression... . . 
I will premise one or two remarks which I have to 
make on the system of training adopted by saying that 
in Germany, as no doubt you all know, every young 
man is compelled by law on entering a trade to attend 
classes for instruction. Such classes the boys employed by 
Zeiss, of course, attend. A certain number of apprentices are 
taken who have, in addition, to attend higher classes, and from 
whom a higher standard of preliminary knowledge is required 
(that is, they must pass that examination which reduces the term 
of service in the army to one year). These higher classes are, 
however, open to the ordinary working boys, if they have 
sufficient brains to avail themselves of them. The teaching of 
optical subjects in the technical school of the town is practically 
under the firm’s control, being subsidised by them, and some, if 
not all, of the teachers being drawn from the works ;.half the 
time spent at this school is during working hours, and is counted 
the same as attendance at the works. ... . 
This training of the boys and apprentices, the scientific 
management of the business and the experimental work is 
supervised by a staff of no less than eighteen mathematicians, 
physicists and chemists, each of whom holdsa University degree ; 
the salaries of these gentlemen, together with the cost of the 
experimental work undertaken, reach a total of from 6000/. 
to 10,0007. per annum. Here, then, in my opinion, you have 
the secret of German progress—a thorough well-grounded 
elemendary training of the workmen, controlled and employed 
by those possessing a read sczentific training. 
A STEREOSCOPIC METHOD OF PHOTO- 
GRAPHIC SURVEYING.) 
IN the method proposed in this paper, photographs are taken, 
with a surveying camera, at a pair of points, the plates being 
exposed in the vertical plane passing through both stations. A 
réseau, or a graduated back frame, gives the means of measuring 
the coordinates of any point on the plates with reference to the 
1 A paper read on October 2, 1gor, before the South African Philosophical 
Society, by Mr. H. G. Fourcade, Forest Department, Cape Town. 
NO. 1701, VOL. 66] 
I am afraid the numbers given |, 
optical axis of the camera. After development and fixing, the 
negatives, or positives from them, are viewed in a stereoscopic 
measuring machine, which, by combining the pictures, renders 
possible the instant identification of any point common to 
the pair of plates. Movable micrometer wires traverse 
each field, and pointings may be made simultaneously with 
both eyes. The readings of the micrometers, referred to the 
réseau, give the three coordinates of the point by direct multi- 
plication by, or division from, constants for the plates, which 
depend only on the focal length of the camera lens and the 
length of the base. When a sufficient number of points have 
been plotted from their coordinates, contour lines may be drawn. 
Theory of the Method.—Let a and B (Fig. 1) be the ends of 
i) 
23 A. 
Fic. 1. 
the base and Q and q’ the positions on the photographs of any 
point P. 
Take A as origin and A B as positive direction of +-axis. 
Let (X, Y, Z) be the coordinates of P ; (xa, fj 2a)(%0 /; 25) the 
coordinates of Q and Q’. 
The equation of A P is: 
HAY | s 
Geez: 
and if we put y=/, we get: 
76 a . xX 
te 7 
Similarly the equation of B P is: 
bed pe apie 
NSAN Ye Z=z) 
where } and / are the x and < coordinates of B. 
Whence, 
a= J(X —6)+6 
a= L(Z- h) +h. 
From these equations we find _ 
Xq-—xXyt+b= Vv =; 
eis the stereoscopic difference, constant for points in any plane 
perpendicular to A y and vanishing for points at infinity. 
The values of the coordinates of P follow : 
ie 
é 
x= dhe, 
é 
ee 
2a 
A check is afforded by the values of X and Z derived from 
BP. 
b 
X= 45-0 
e 
b , 
— eet 
x’, and 2’, denoting here the coordinates of Q’ referred to B. 
