nV THE CONSTUrCTION OF THEATERS. 30 J 



tf.ov^gh E, PI. VU, ill the middle of which a small maho- 

 gany table D was made fast by a screw, for the purpose of 

 supporting the animal under the bell glass A. Two holt-j 

 were made through the table f«)r the insertion of tubes to sup- 

 ply and take off the air, each of them communicated with 

 one of the mercurial gasometers; the tube B deliver-ed gas 

 towards the upper part of the glass A, in order to bring th* 

 supply of fresh air near the head of the animal: the open- 

 ing of the tube C was placed within half an inch of the ta- 

 ble to convey off the respired air; the gasometer connected 

 with this tube was made to communicate with a m^^rcurjal 

 bath G, in which portions of the respired air were pre- 

 served for examination. Quicksilver being poured into the 

 trough E, so as to rise to a level with the top of the maho- 

 gany stand, we placed a Guinea pig upon it, with the bell- 

 glass over him, and as its edges were immersed in quicksil- 

 ver, the animal was completely confined in atmospheric air; 

 we foMud that his body occupied the space of 39 cubic itiches, 

 which, deducted from the cubic contents of the glass A, 

 left 55 cubic inches for the air confined with the pig, to 

 which must be added 5 more for th«t coDtaiuedi in th* 

 tube C. 



fTo be <:on<:lud€d in our n^xt.J 



X. 



On the Construction of Theatres, so as to render them secitrf 

 against Fire. In a Letter from Mr. B. CooK. 



I 



To Mr. NICHOLSON, 

 SIR, 



JLN some former letters you did me the favour to insert in Iron rcc<m- 

 your Journal, 1 have recommended the use of iron in the "^^^^ '-•^in^t,<.i<j 

 place of wood ; in my last on that subject I pointed out its 

 use and advantages in substituting it for wood in buildings, 

 but more particularly in adopting it for staircases, as pro- 

 misijig a certain escape in case of fire. What 1 would di- 

 rect the attention to in this is, the great advant-age of enj- 



pioyinif 



