42 Mr. C. Holthouse on Increasing the Light 



flame in the same proportion become steadier and more uni- 

 form, till at seven inches, which was the length of the pillar 

 of this chimney, it was as steady as could be desired. One 

 fact was strikingly obvious during this experiment, viz., that 

 the increase of brilliancy was by no means commensurate 

 with the loss of light occasioned by the smaller bulk and 

 great unsteadiness of the flame. From several trials with 

 chimneys of various lengths, I should say that a seven inch 

 pillar, for an Argand burner of the ordinary size, is well 

 adapted for giving brightness, and at the same time steadi- 

 ness, to a flame. 



To ascertain the best diameter for the chimney, eight pieces 

 of tin were procured, each two inches square, and having a 

 circular aperture in their centre, varying from one and a half 

 to half an inch in diameter; these, by turns, were fixed to the 

 moveable stage of a microscope, and then placed directly over 

 the flame of a lamp, so that the centre of the circle of the Ar- 

 gand burner should correspond with the centre of the circular 

 aperture in the tin; a simple* glass chimney being now placed 

 upon the tin, the whole apparatus was lowered till the flame of 

 the lamp passed through the aperture in the tin. By trying the 

 different sizes one after the other, we were able to decide upon 

 that which gave the greatest degree of illumination, and by 

 raising and lowering the apparatus over the flame, the best 

 height from the level of the wick for obtaining the greatest 

 light was determined. The following are some of the results. 

 The size of the flame was in a direct ratio with the size of the 

 aperture in the tin, but its brilliancy was in an inverse ratio ; 

 in other words, the flame diminished in size but increased in 

 brilliancy as the aperture through which it had to pass was 

 lessened. The effect produced by chimneys of different dia- 

 meters, but of equal length, provided the aperture in the tin 

 over which they were placed remained the same, was so tri- 

 fling, that it was scarcely appreciable : the diameter of the 

 aperture in the tin being, for instance, one inch, and that of 

 the chimney the same, no material alteration in the brilliancy 

 or bulk of the flame was produced when a chimney of double 

 the diameter was substituted for it. I need hardly observe, 

 that the diameter of the chimney must not be less than that of 

 the tin. I said at the commencement of this letter, that there 

 was a limit beyond which we could not increase the bright- 



* When I apply the term simple to a chimney, I wish to be understood 

 as speaking of those cylinders of uniform diameter from end to end; those 

 composed of two parts, I shall, to prevent unnecessary tautology, designate 

 compound. 



