340 Mr. J. Bridge on the Gyroscope. 
core is very great compared with the thickness of the primary 
wire. Secondly, I have found that the size of the condenser 
must be increased with the conducting power of the primary 
wire. Thus a thick primary wire requires a larger condenser 
than a thin one; a primary wire of copper requires a far larger 
condenser than one of iron of the same length and thickness ; 
and a very short primary wire of any metal requires a condenser 
very much larger than that which is necessary for one of 
the same metal 100 feet long. I have found that when the pri- 
mary wire is not more than 30 feet, a condenser of moderate 
size will not produce the slightest effect on it. Thirdly, I have 
found that when a condenser is very much larger than that 
which is required to produce the full effect of a condenser on a 
given coil, it not only does not increase the power of the coil, 
but it makes it less than it would be without a condenser, and 
sometimes destroys it; and that in general there is a limit 
to the size of the condenser, beyond which its effect on the coil 
will be diminished. Fourthly, I have found that a condenser so 
large as to diminish the power of a coil excited by one cell, will 
increase its power when the coil is excited by ten or twelve cells. 
Hence the same condenser will not answer for the same coil 
when batteries of very unequal powers are used. Then, every 
condenser should be made in such a way that the entire of it 
will produce the full effect of a condenser on the coil for which 
it is intended when the largest battery we wish to use is em- 
ployed, and that a small or a large part of the condenser may 
be used when we wish to excite the coil by a weak or strong bat- 
tery. I learned from Mr. Gassiot and M, Foucault during the 
late meeting of the Association, that they were aware of the ne- 
cessity of making the condenser in this way. 
Maynooth College, 
Sept. 29, 1857. 
P.S. I have abstained from saying anything about the pri- 
mary coil, because my experiments on it have not led me toa 
satisfactory conclusion, and not because I think the primary coils 
in common use incapable of improvement. I believe that they 
are very badly calculated to attain their object, and that they 
have been made on a false principle. 
XXXIX. On the Gyroscope. By Joun Brivez, M.A.* 
HE gyroscope, as usually constructed, consists of a solid of 
revolution, whose axis forms a diameter of a circular ring 
into which its extremities a, a’ are inserted: this ring is move- 
* Communicated by the Author. 
