2 . Mr. Armstrong on the Efficacy of ae 
Number of discharges obtained per 
minute when it was applied to the -220 
insulated boiler .....seeceeeeescescesens 
The discharges were so exceedingly rapid when the elec- 
trometer was connected with thé boiler, that it was difficult 
to count them with accuracy, but the number I have inserted 
is assuredly not overstated. ; 
The boiler is a wrought-iron cylinder, with rounded ends, 
and measures three feet six inches in length, and one foot six 
inches in diameter. It rests upon an iron frame, containing 
the fire, and the whole apparatus is supported upon glass 
legs to insulate it. The application of the fire is unfortunately 
very imperfect, in consequence of which the boiler will not 
maintain, for any considerable time, the discharge of steam 
which is requisite to produce the effects I have mentioned, 
but a short interval of quiescence suffices to restore the press- 
ure, and to render the boiler again ready for action. 
It is much more convenient and effectual to collect elec- 
tricity from the boiler than from the steam-cloud, but in 
order to obtain the highest effect from the boiler the electri- 
city of the steam must be carried to the earth by means of 
proper conductors. 
Notwithstanding the enormous dissipation of electricity 
which is occasioned, when the tension is great, by the dust 
and eflluvia of the fire, and by the angular parts of the ap- 
paratus, I can draw sparks, twelve inches long, with great 
rapidity from the rounded ends of the boiler; and if a projecting 
ball of proper dimensions were attached to the apparatus, 
much longer sparks would probably be obtained. 
I find it essential to a high development of electricity, that 
the steam should be discharged with a slight intermixture of 
water, although, from a cause which it is needless to explain, 
this did not appear to be the case in the experiments which 
I formerly made with a gun-metal generator. 
A piece of hard wood, such as ebony or partridge wood, is 
the best material I have yet tried in which to make the dis- 
charging passage, but it is chiefly by prefixing to the wooden 
channel, a brass cap, of very peculiar construction, that I have 
been enabled to obtain the present powerful effects. The 
piece of wood containing the discharging passage, is, for the 
convenience of fixing, formed into a plug such as is repre- 
sented in fig. 1. The brass cap, to which I have just alluded, 
is affixed to the smaller extremity of the plug, and is shown 
in that position in the drawing. Fig. 2 is a longitudinal sec- 
tion of the same, drawn to the full size, and exhibits the hole 
through the wood, and the internal structure of the cap. The 
