214 ECONOMICAL LAMP. 



rain water to the boiling point ; and the third, the time required 

 by calculation to produce the same effect ; taking the first expe- 

 riment for the standard, viz. that with eight burners, the lamp 

 will make 1000 grs. of water boil in 3| m., which is very nearly 

 half the time which it requires to make 2000 grs. boil. 



The real times are copied exactly from the memoranda I 

 made while performing the experiments ; and I was much sur- 

 prised to find how nearly they coincided with the times by cal- 

 culation : especially since the watch used had no seconds hand. 

 In the last experiment but one the water never boiled strongly ; 

 and in the last it only just simmered. I have added a sketch 

 and description of the latnp, for the use of those who may 

 wish to procure one like it. Its dimensions are exactly double 

 those of the drawing ; with the assistance of which any tin- 

 cumed faster '^^^ ^'^^ ^® ^^^^ ^° make it 3 and I should reconqmend it to be 

 •without aug- made with a reservoir, to prevent the oil from being m.ach heated, 

 feet" '"liencea ^^ "'^ ^■'^^^ ^^'^"'^ ^^ experiment, that this circumstance consi- 

 reservoir is ad- derably increases the quantity of oil consumed in 9 given time, 

 ▼uable. without adding, in the least degree, to the heat of the lamp. 



The price of one^ similar to the drawing, will not exceed Is. 6d. 

 exclusive of the glass, which is about one tenth of the price of 

 the commonest Argaqd lamp that I have seen. 

 I am. Sir, 



Your constant Reader, 



L. O. C. 



Description pi. V, fig. 3, 4. A the body of the lamp 3 B. B. 

 the burners ; C. tube for conveying air to the flame ; D. D. D. 

 small feet which raise the body of the lamp, and allow the free 

 access of air to the tube C. ; E. E. bended wires, which support 

 the glass F. } G. small tube for filling or emptying the lamp*. 



* It would afford an acceptable result, if the writer would also mea- 

 sure the light afforded by the lamps under comparison, as well as the 

 heat. As the method of shadows, though very simple and easy, is cer- 

 tainly not in general use, I would here repeat, that when the shadows 

 of the same object, projected upon a wall or surface by two lights, are 

 equally dark, the lights themselves are equally intense — that, if not, the 

 darkest shadow will be projected by the interception of the brightest of 

 the lights ; and that, if this brightest light be then removed farther from 

 the wall, till both shadows become equally dark, and the distances of 

 the lights from the wall be in that situation measured, the intensity of 



each 



I 



