SCIENTIFIC SUMMARY. 
89 
conductivity of carbon, and the way it is affected by temperature. He finds 
that of gas retort carbon at 0 deg. = 00136 if mercury = 1 — and the co- 
efficient of increase of conductivity 0'000345 per degree Celsius. The arti- 
ficial carbon rods produced by compression of carbon powder also show 
greater conducting power with increasing temperature, but the increase is not 
so great as in retort carbon. The electric conductivity of gas-carbon and its 
variability under pressure has been re-examined by MM. Naccari and 
Pagliani, and in such a way as to throw some doubt and some light on the 
theories advanced respecting the common microphone. Carbon prisms were in- 
serted in a Wheatstone’s bridge to determine their resistance. When subjected 
to great pressures the resistances of the rods of carbon showed scarcely any 
change. Hence it appears that the changes of conductivity which carbon 
exhibits in the microphone and in the carbon telephone under varying pres- 
sures, are due to mere changes in the external contact. 
The similarity of Sulphur to Selenium in respect of its variable con- 
ductivity, is stated to be among the results of Prof. Graham Bell’s recent 
researches, but only at temperatures below that at which it becomes dark 
and viscid. 
Incandescent Electric Lights have been made successfully by Mr. Swan, 
of Newcastle-on-Tyne. The material used by him is a wire of dense and 
elastic carbon, made by a process which has not yet been disclosed. Each 
is about three inches long, about of an inch in diameter, and so light as to 
weigh only from to of a grain. Their durability is remarkable, as he 
states that lamps have been continuously lighted by them for over three 
months at a time, with an intermission of only three weeks. The light 
varies in intensity from 30 to 50 standard candles. Thirty-six such lamps 
were exhibited at his lecture, working from a dynamo-electric machine 
driven by a four horse-power engine. At a previous lecture, twenty lamps 
gave more light than the seventy-six gas jets usually supplying the room. 
Fitzgerald 1 s Magneto- andDynamo-Electric Machines. — The improvements 
in magneto- and dynamo-electric machines, the invention of Mr. Desmond 
G. Fitzgerald, deserve careful attention, inasmuch as they show a decided 
advance in the right direction. The main idea of the inventor seems to 
have been to aim at perfecting the Gramme machine ; and so, instead of 
rotating the ring between the poles of a magnet on the ordinary system, he 
wholly or partially surrounds the ring both longitudinally and transversely, 
thus increasing the effective inductive action. The ring is thus magnetized 
directly, and with the least possible loss, and the direction of the inducing 
magnetic polarity is in the circle constituted by the ring itself, as it 
should be. 
Considerable modifications are made in the construction of the ring. 
Ordinarily, in winding a number of coils of wire upon a ring, more especially 
if it be of circular section, and if the number of turns of wire be the same 
in each layer, interstices are left between the coils. These interstices are 
filled by Mr. Fitzgerald with soft iron wedge-shaped blocks. These blocks 
can either be made with the ring, or separately, and slipped on, the ring 
being made in halves to receive them. 
The Metric System. — There has lately been some agitation in the United 
States as to the advisability of rendering the Metric System compulsory for 
