4.62 Prof. A. W. Riicker on the Self-Regulation 
who may alter them to his sight, and yet have them in perfect 
order for yourself by bringing the index to your own mark. 
The increase of power in the glasses, and of comfort to the 
user of them, has been a surprise to almost all who have tried 
the improved adjustment. 
I do not enlarge upon the way in which Mr. Browning 
has carried out the details ; you can see for yourselves that 
the improvement in no way disfigures the glasses, and as the 
expense is 12s. 6d. for glasses made to the common pattern, 
I think that the improvement is within the reach of most 
people who use binoculars. 
LIT. On the Self-Regulation of the Compound Dynamo. 
By A. W. Rooker, W.A., P.RS.* 
f Biew theory of the self-regulating power of the compound 
dynamo has not been treated in a satisfactory manner 
in any discussion of the subject with which I am acquainted. 
Some conclusions as to the proper method of constructing 
self-regulating dynamos have been drawn from equations in 
which the power of perfect self-regulation is assumed. As 
this perfection is known to be unattainable, no great weight 
can be given to arguments based on the assumption in ques- 
tion, and it will in the following paper be abandoned. A 
further inquiry will also be entered upon, viz. how far the 
conditions of good self-regulation are consistent with the other 
desiderata aimed at in the construction of a dynamo—such, 
for instance, as high efficiency. 
The entire investigation will be based on Frolich’s equation, 
which expresses the electromotive force in terms of the 
current and the constants of the machine, and will therefore 
not apply in cases where the prejudicial effect of the magne- 
tization of the armature is apparent. The notation and 
diagrammatic representation of the machine are those which I 
have found useful for teaching purposes. 
Let the points A, X, Y be joined jp goa 
by three straight and three curved 
lines. | 
Let the side X Y represent the 
armature of the machine. The 
points A, X, and Y may be called OC 
its terminals. The curved lines Pa 
represent the magnetizing coils of ,2-~ _"-\ y 
the inducing magnets ; the straight 
lines A X and AY represent external resistances. 
* Communicated by the Physical Society: received March 24, read 
April 25, 1885. 
