Mr. Cuttriss the gave a lecture on the Electric Light – What it is, How it is produced
Mr. Cuttriss first enumerated the various sources of Electricity & then gave a general description of the better known arc & incandescent system of illumination, including among the former the Jablochkoff & Brush Lights, and among the latter Edison & Swan’s. The Arc System is more especially applicable to large buildings & open spaces; the incandescent lamp being adapted for smaller rooms, such as would be met with in private houses.
The lecturer then exhibited and described a Dynamo machine, now such an important factor in connection with Electric Lighting for, though galvanic batteries will answer on a small scale it is to that machine that we must look for the future development of this new light. The Dynamo machine is essentially an apparatus for the conversion of mechanical force into Electric Force. It is an instrument in which an armature is caused to rotate very rapidly between the poles of one or more electro-magnets , termed field magnets.
Starting with the residual magnetism of the Field Magnet the at first feeble current produced in the armature wires by the rapid cutting of the magnetic lines of force during rotation is gradually intensified by the increasing magnetism generated in the field magnets through the circulation of the current round them. This accumulation goes on until the magnets are sufficiently charged, if the speed of the machine be then maintained at a regular rate, a uniform current insuring a steady light results.
The intensity of the light within certain limits being proportional to the speed of the machine. By means of a hand Dynamo machine Swan Lamps of 5 – 10 & 20 candle power were exhibited in operation; their mode of construction was also explained. The Swan Lamp consists of a glass globe of one and a half to two inches in diameter, exhausted of air in the most perfect manner known & hermetically sealed. Enclosed is a loop of carbon, formed by carbonising a piece of cotton thread by a special process; this loop is attached to two platinum wires passing through the lower part of the globe & forming a connection with the machine. When a current is passed through the wires, the resistance offered by the carbon thread (carbon being a bad conductor of electricity) causes it to become so intensely heated so to evolve a very brilliant light & as the globe is free from air, the carbon does not burn away as it would under ordinary conditions.