1814,] Philosophical Transadlms, Part II. 1813. 381 



quent and more destructive than formerly, especially about New- 

 castle and its neighbourhood ; or rather I believe they are not nov(r 

 so carefully concealed as they used to be. 1 consider the mode of 

 ventilating the coal mines, at present practised, as exceedingly de- 

 fective, and have not a doubt that they might be so contrived as to 

 be kept perfectly free from all such accidents, without any addi- 

 tional expense to the proprietors. But I have little hopes of seeing 

 such improvements attempted ; because they are considered as inju- 

 rious to the interest of certain persons at present employed in coal 

 mines, who will have address enough to convince the proprietors of 

 such mines that all attempts at new methods are absurd and nuga- 

 tory. While the present very absurd mode is continued, Dr. 

 CJanny's lamp, which is equally simple and ingenious, might be 

 employed to diminish or destroy the danger of explosions. It is 

 merely an air tight lantern, containing a candle, which is kept 

 burning by means of a current of air blown through it by a bel- 

 lows. If the air contains such a quantity of inflammable gas as to 

 explode only the portion within, the lamp would burn, and thus 

 the workmen would escape danger. Such lamps it is true would 

 be much more expensive than the present mode; but they would 

 save the lives of hundreds of workmen who at present fall victims 

 to these destructive explosions. 



7. On the Light of the Cassegrainian Telescope compared with 

 that of the Gregorian. By Captain Henry Kater, Brigade Major. 

 Major Kater was enabled to compare these two telescopes with each 

 other, in consequence of the excellency at which a self-taught 

 artist in Ipswich, named Crichmore, had arrived in making these 

 instruments. Several of each, in every respect of the same good- 

 ness, were within the examination of Major Kater. The result 

 was, that with an equal aperture, the light of the Cassegrainian* 

 telescope was to that of the Gregorian as G to 3*3. He conceives 

 ihc dili'erence to arise from this circumstance. In the Gregorian 

 telescope the focus of tiie rays from the great mirror is at the small 

 mirror, while in the Cassegrainian telescope the rays from the great 

 mirror arrive at the small one before they reach their focus; hence 

 in the first they cross each other, but not in the second. Now 

 when thus crossing, they may interfere with each otlier, or they 

 may repel each other, and thus occasion the dissipation of a quan- 

 tity of the light. 



8. Additional Observations on the Effects of Magnesia in pre- 

 venting an increased Formation of Uric Acid ; with Remarks on 

 the Influence of Acids on tiie Composition of Urine. By William 

 Thomas Brande, Esq. F. R.S. Prof. Chem. R. 1. The use of mag- 

 nesia when the urine deposites red sand, or has a tendency to form 

 calculi composed of uric acid, was first suggested by Mr. Hat- 

 chett ; and it appears from two cases related in this paper, that it is 

 attended with tlie happiest effects. It docs not prove injurious to 

 the stomachy nor duci it excite irritation in tlic bladder, as is the 



