of the Compound Dynamo. 479 
I have seen a solution of the question with which it deals, 
published by Dr. Froélich in the current number of the Elek- 
trotechnische Zeitschrift, April 1885. I should like, there- 
fore, to add a few words as to the relations between our 
investigations in respect both of time and result. 
The method and chief conclusions given in my own paper, 
including the formule for ¢, g, and the mechod of finding 
limits to the perfection of the regulation, were given to my 
Senior Class in Technical Electricity in February last. In 
March I had several engagements which made special calls 
upon my time, and partly on this account, partly because I 
wished to add a discussion of the case when Q or B is nega- 
tive, I did not publish my results at once. 
Towards the latter end of March I received my copy of the 
Eilektrotechnische Zeitschrifé for that month, which contained 
the first part of Dr. Frolich’s paper. In that he gave the 
formule for the electromotive force, current, &c. in the cases 
of the series, shunt, and both forms of compound dynamo, in 
terms of the external and other resistances. The formule 
were not reduced to any simple form like the equation in } 
given by me; and though the paper showed that Dr. Frélich 
was engaged on the question of self-regulation, it did not 
afford any indication of his method of attacking the problem. 
The next day after seeing this paper I sent my own investi- 
gation to the Secretary of the Physical Society. It was 
- brought before the Council of the Society on March 28th ; 
but as it was thought that the matter was of some interest, 
the reading of the paper was postponed till the first Meeting 
after the Haster vacation (April 25th), and I was asked to 
attend for the purpose of giving an account of it myself. In 
the interval I made some improvements in the statements as 
to the physical meanings of the inequalities which I de- 
scribed at the Meeting, and have incorporated these in the text. 
It is only since the paper was read that I have received the 
April number of the Elektrotechnische Zeitschrift, from which I 
learn that Dr. Frolich has “seit dem Abdrucke des. ersten 
Theiles dieses Vortrages,’ and guided partly by theory, 
-partly by experiment, arrived at a very satisfactory solution 
of the problem of obtaining a constant external electromotive 
force. 
As far, therefore, as our work is common, I do not wish to 
question Dr. Frélich’s undoubted right to claim prior publi- 
cation. The above statement is, however, necessary to show 
_ that my results were obtained independently. 
On comparing the two papers, it will be seen that I have 
throughout considered the ee with reference to the 
2K 2 
