Tf^aier hy the Ele^ric Explofion. 247 



Thefe are tlie direftions for making die experiment ; but the rationale of it cannot be 

 underftood unlefs the nature of the iriti-rriipied explofion ht explained; becaufe I believe books 

 on eleiSricity do not contain the neceflary information. It muft be confidered, in the above 

 experiment, that if in place of water the tubes be filled with air, the whole of the charge 

 ef the Leyden jar will pafs, at each explofion, from the upper to the under wire, and no in- 

 terruption in the difcharge will happen ; but if they are filled with water, then an inter- 

 rupted dtfcharge may be caufed ; by which is meant that a part of the charge only paffes at 

 each explofion through the water, from wire to wire, and with much diminifhed velocity. 

 The refiduary ele£lricity in the Leyden jar is nearly one half; as maybe accurately de- 

 monftrated from the difference in point of denfity, elafiicity, and conducing power of the 

 medium of water and air as already obferved. It muft be added, that although water in 

 large quantity is a good condu£lor, and air is not ; yet water being here in very fmall 

 quantity, it proves a bad conduftor, as is the cafe with the very beft conductors. A cubic 

 foot of water is only juft capable of receiving, or letting pafs through it, a full difcharge 

 from a jar of one foot of coated furface ; and the quantity of water employed in this experi- 

 ment not bemg ToisVooth part of a cubic foot, it is a very imperfeft conduflor; fo that an 

 interrupted difcharge only can pafs through the tube, without difperfing the whole of the 

 water. But if the difcharge be not feemingly as ftrong as the tube can bear without break- 

 ing, the gaz is not produced from it ; and on this point hinges this extremely delicate 

 procefs. 



The fituation of the different parts of the above defcribed apparatus is (hewn by Fig. 5. 



To fucceed by the method of the complete ox uninterrupted explofion, the following apparatus- 

 muft be ufed, and rules obferved : 



I. A tube (Fig. 6.) ij employed, about four or five inches in length, and i-5th or i-6th 

 of an inch in diameter. One end is mounted with a brafs cap (Fig. 7.), and the other end 

 is fealed at the lamp, with a wire about i-4cth of an inch in thicknefs fixed into it, as above 

 defcribed ; which extends into the brafs cap, fo ^ to be almofl in contaft when the explofion 

 lo made. If the wire touches the brafs cap there will be no explofion. The tube being 

 filled with, and fet in, a cup of water, the difcharge may be made into it as in the above, 

 defcribed procefs ; but here the infulated ball muft be placed at a greater diftance from the 

 prime conductor, and a Leyden jar, with only 50 fquare inches of coating, will anfwer the 

 purpofe. In this way of making the experiment, gaz is produced by each difcharge in the 

 brafs tube, and in much greater quantity, and with much lefs frequent accidents, and lefs 

 trouble, than in tlie former method with the interrupted difcharge. But the gaz obtained 

 with this apparatus always contains a larger proportion of atmofphcrical air, on account of 

 the quantity of water, and more immediate and extenfive communication of it with the 

 atmofplicre. By repeated difcharges there is an impreffion made in the brafs tube, in the 

 part where the difcharge pafii.-s through it, and at bit a fmnll hole is made In that part. 

 On this account tlie fame mounted tube cannot ferve for producing a l.irge quantity of 

 gaz. 



The other fort of apparatus invented by Mr. Cuthbcrtfon is reprefented by Fig. 8. At 

 firft it confifted of a glafs tube half an inch wiilc and about five inches in length, mounted; 

 at one end with a brafs funnel, and inverted in a brafs difli ; but afterwards the tubfc was- 

 blown funnel-wife at the end, as (liewa by Fig. 9. The other end muft. have a wire 



about 



