444- l:ij!runlitisf:r Decomprjiiig 



«hod, shhoug}! hot f© explained, of Mr. Van Trooflwyk. And tlie otlier metlio<l is by means 

 %l the uinnUrrufltA or complete ex^lofion ; for which there are two different kinds of ap- 

 paratus. Thcfe were invented by Mr. Cuthbcrtfon in the ccuife of my inveftigacion of this 

 fubjeft. 



To faccecd by the method of tlie in/t'rrnpteJ exphjion, ti.e following arc the neccdii y parta 

 -of the apparatus to be ufed, and the circumllances to be aitendcd to : 



I. The eUnrical machine iniift psjj'efi fiij^cienl potter. I do not think any cylindrical machine 

 can be made to anfwer in this procefi, if a large quantity of gaz be required ; becaufc they 

 cannot be msde to afl with due regularity, conllancy, and furce. Iiiequ;ility of the furfacc 

 of the cylinder is unavoidable, which caufes undulation. A cylindrical machine never 

 continues in full force above five or fixminutes, without frcfli amalgam. Hence, from the 

 repeated amalgamization, the difcharges wiM be fo va.rjab]e tliat the tubes rauft be frequent]/ 

 broken. 



I ufed plate machines of a peculiar con(lru£llon by Cuthbcrtfon. Thefe machines do 

 rot require frefli amalgamization oftener than once in eight hours, a«d they pofTefs fuperior 

 powers of a£ling, in point of regularity, force, and duration. A plate of 24. inches in dia- 

 meter, with a jar containing 150 fquare inches of coating, afforded an adequate difcharge 

 every fccond or third revolution, for feveral hours; and for a ftill longer time every third or 

 fourtli revolution, with one application of amalgam. A 31 inch plate machine allurded a 

 due difcharge at firft every revolution, and afterwards every fccond revolution for man/ 

 hours, with one application of amalgam. The moft ufeful and expeditious machine was 

 that with two plates, each 24 inches in diameter, and fimilar to that of Teyler. It produced 

 25 difcharges every 15 revolutions for an hour or two; and for four or five hours longer 

 a difcharge was produced by lefs than two revolutions, with one amalgamization. 



2. The Leyden jar muji have a fiiffic'ient quantity of coaled furfftce : \vithoUt which the dif- 

 charge will not be fufficiently powerful to produce the gaz required. The proper quantity, 

 as found by experience, was about 156 or 160 fquare inches, with an ufual proportional 

 prinve conduftor. 



3. The dijlance betivecn the iiifulated hall, and the prime conduBor, miiji aTivays he lefs than 

 the dijlance between the extremities of the ivivcs. Not the Icafl notice of this circumftance 

 has been taken ; yet without attention to it the experiment can never fuccecd, or only for 

 a very fliort time. Accordingly, as the diftance between the extremities of the wires within 

 the tube anfwered bed when it was 5-8ths or 7-8ths of an inch, the diftance hctweea 

 the infulated ball and prime condu£lor was feldom more, but frequently lefs, than 5-8ihs 

 or 6-8ths of an inch. The eye muft be kept upon. the fparks within the tube, and by prac- 

 tice a pcrfon may become a judge of their force by their vividnefs ; which will direct; him 

 to bring the receiving ball nearer to the prime condudor, when there appears danger of the 

 tube being broken ; and on the contrary, to remove them to a greater diftance from one 

 another when the fparks do not produce gaz duly from the water. When the difcharge is 

 of tlie moft produ£live force, both ends of the wire within the tube will be illuminated by a 

 fpark; but, when it is weaker, one end only of the wire will be illuminated ; and when 

 this is the cafe, there is no rifque of the tube being fra>fturcd, but gaz will rife from the 

 end of one wire only inftead of two. 



4. The extremities of the np^er and under ivire -within the tiite mufi Ic at a certain diftance 



5 /rcHj 



