Incandescent Lamps. 8& 



of battery power, and rendered incandescent. The arrange- 

 ment I made is of a mnch simpler construction, gives a 

 perfectly pure light, and develops less heat. It consists of 

 an electro-plated outer tube nine inches and a half long by 

 eleven-sixteenths inch external diameter, glazed at one end 

 with a stout piece of plate-glass, made perfectly secure and 

 tight. 



" A Swan's electric lamp is used — the filament of which 

 is carbon, and rendered incandescent by means of battery 

 power. It is hermetically sealed in a glass shade ; and 

 water, conveyed to and fro through very small brass tubes, 

 is made to circulate round the lamp. The light from this 

 lamp is perfectly pure, and exhibits the conditions of things 

 in their true and natural colour. For prolonged observation 

 I should prefer to use either a Grove's or Bunsen's battery, 

 but in the demonstration just referred to four cells of a 

 modified Leclanche battery were employed, and answered 

 admirably. It is advisable to have as great a pressure as 

 possible for the water supply, so as to ensure perfect circula- 

 tion, and for this I suspended from a hook fixed near the 

 ceiling of the room a tin can containing water, connecting it 

 with the brass tubes by means of lengths of India-rubber 

 tubing." 



Dr. Lodge gives an account of an operation he performed 

 with the use of the apparatus just described, and appears to 

 have been impressed with its value. 



For examining the mouth and throat the small Swan lamp 

 appears most valuable, and it is also likely to prove a useful 

 accessory for dentists, and to replace the somewhat cumber- 

 some mirrors in use by them. A very small amount of battery 

 power is required to obtain the necessary illumination. 

 Probably in the surgery a form of " Gravitz battery," such 

 as Sir William Thompson's, or a modified Leclanche, would 

 be the most convenient, but where space is an object a 

 small bichromate battery will give good results for a short 

 time. The modified Leclanche exhibited will last without 

 any attention, except adding a little water now and then, 

 for at least twelve months, and will always be ready for use. 

 It has, however, the drawback of polarising quickly, and 

 therefore the lamp must not be kept in use for more 

 than three or four minutes at a time without giving the 

 battery a similar period for rest. Probably in many instances 

 this form of battery would be sufficiently effective. For 

 portable purposes, a small form of bichromate battery would 



