Mr. J. G. Children oji a New Light for Optical Purposes. 1 79 



and adaptation of which its accuracy depends, are, — 1st, the 

 screw, the convolutions of whose thread must be of geome- 

 trical uniformity; 2nd, the cone, whose surface must be of 

 geometrical truth ; and 3rd, the wheel, whose edge must have 

 so intimate a contact with, and hold upon, the surface of the 

 cone, as to partake accurately in its motion at every point 

 which it traverses. 



My experience in the use of a similar cone and wheel in a 

 steam indicator constructed at the expense of the British 

 Association of Science, has convinced me that the required 

 accuracy is in this last respect attainable. 



In respect to the two first-mentioned sources of error, it 

 may be observed that there are no mechanical forms of greater 

 simplicity than the cone and the screw, and probably none in 

 respect lo which greater truth of construction is attainable. 



Every such instrument must however have its error ; its 

 amount in respect to this instrument maybe determined by an 

 obvious method, and it is probable that it may in every case be 

 corrected by a corresponding adjustment. 



XXXI. 071 the use of a mixture of Spirit of Wine and Cam- 

 phine, as a Light for Optical Purposes. By John George 

 Children, Esq..) F.R.S. 



To Richard Taylor, Esq. 

 My dear Sir, Halstead Place, Feb. 13, 184>. 



TF you think the following trifle worth inserting in the Phi- 

 * losophical Magazine, it is at your service. 1 have lately 

 assisted a friend in getting up an apparatus for dissolving 

 views, &c. on a scale too large for sufficient illumination by 

 the best Argand lamp, and we considered condensed hydrogen 

 gas as too dangerous an agent for a plaything; especially in 

 private houses in the country, where much must be left in 

 the preparation of the gases, &c. to servants unused to such 

 duties. We set to work therefore to find a substitute that 

 might answer our purpose; and after a few trials we obtained 

 a tolerable light, by throwing the flame of spirit of wine on a 

 surface of quicklime by a current of oxygen gas, something 

 after the manii' r of Lieut. Drummond's original experiment*. 

 The illumination by the flame of spirit of wine alone, however, 

 proved to be too feeble; but by mixing a portion ofcamphine 

 (spirit of turpentine) with it (which readily dissolves in alcohol) 



• Philosophical Transactions, 1826, p. 330. Drummond's object and 

 ours were Koniewliat dillerent. He wanted to get an intense but small 

 bphere of light, " adapted to the nature of a (paribolic) reflector:" we 

 also wanted as intense a light as we could obtain, but, as we could not 

 mlvantageously use a reflector, one which should likewise extend over a 

 much larger surface. 



