VOL. LXVIII.] PHILOSOPHICAL TRANSACTIONS. 33Q 



pasted on the parapet of this model. On the top of the roof in the middle, 

 conductors of different lengths and terminations were occasionally put, just as the 

 experiments required. The scale from which this model was made, when com- 

 pared with the house, was 4- of an inch to a foot. In regard to the wood of 

 which the model was made, I took care that it was well baked, and soaked, 

 while hot, in drying oil, before the several parts were joined together, that it 

 might be the more similar to the bricks and other materials of the building itself, 

 in the power of resisting the passage of the fluid, whenever any attack of it 

 should be made. For brick, stone, dry lime, &c. had been observed many 

 years ago by Mr. Delaval and others to resist the passage of this fluid very 

 considerably. 



In order to move this model with the velocity required, it was necessary to 

 have a frame of wood, of such a length as would suffer the model, with the 

 pointed conductor on it, to be out of the reach or influence of the charge con- 

 tained in the cylinder, both at its setting off, and when it had arrived at the end 

 of its journey. To this frame, 2 upright posts of wood, 10-i- feet long, were 

 fixed at the further end, and at a distance from each other equal to the width of 

 the frame. On the to|j of these posts, and in the middle between them, were 

 fixed 2 wheels of different diameters on the same axis. The larger took the 

 line that was proposed to draw the model, and the lesser another line suspending 

 2 weights which regulated its motion. For after the heavier weight had 

 descended so far as to bring the model directly under the substitute, it was then 

 checked; but the less weight continuing to descend, the model moved forward 

 with its acquired velocity, joined to the power of the less weight. And that the 

 remaining motion miglit at last be overcome, without striking against the 2 

 posts, some narrow slips of cloth, 7 feet long, were nailed on the frame, in those 

 parts over which the model was to pass before it reached the end. This model 

 moved like a sledge, by means of 2 slips of wood fixed at the bottom, which ran 

 in 2 grooves that were cut along the frame from end to end. And the line 

 which drew the model along, was fixed very near the centre of resistance. 



To construct the substitute for a cloud, I first joined together, in 1 3 lengths, 

 the broad rims of 120 drums, merely to have Ihem portable, by means of wood 

 cut mto long slips, which were fixed on their insides: but, as those drums were 

 not accurately of a size, the several joinings were covered over with cloth, and 

 pasted down, to make the surface throughout more even. After this, the 

 whole number were properly covered with tin-foil, excepting 8 ; for these being 

 brass, required to be covered only at their joinings. All these drums together 

 formed a cylinder above 155 feet in length, and above 16 inches in diameter. 

 The whole cylinder was made in 4 separate parts: 3 of those parts could easily be 

 .made to communicate, or not, with each other: the 4th, being brass, was 



X X 2 



