338 PHILOSOPHICAL TRANSACTIONS. [aNNO 1778. 



wire joined to one end of it, that should, when extended properly, consist of 

 several hundred yards. This idea leading to an expence too considerable for 

 an individual, I presumed to hope for other assistance. 



Upon an humble preesentation of these matters, his majesty, who is always 

 disposed to promote every pursuit which tends to the advancement of science 

 and the good oof the public, most graciously condescended to encourage the 

 undertaking; and, by the favour of the right honourable and honourable Board 

 of Ordnance, I was immediately enabled to carry the intended plan into execu- 

 tion. Very soon after this encouragement, I procured cori-ect drawings of the 

 building called the Board-house at Purfleet: from these an exact model was 

 made, excepting the windows and doors, which were omitted, because they were 

 immaterial on this particular occasion. In this model, a strict attention was paid 

 to those parts of the building where metal had been introduced; such as the 

 hips and gutters of the roof and the several spouts to carry off the water. And 

 as the north-east corner of the house was the part that sutlered by lightning in 

 May last, particular attention was paid to the two cramps at that corner, and the 

 two spouts on the north-side. These cramps, in the model, were made of 

 small wire, that bore nearly an exact proportion to those in the building itself; 

 not only in regard to length and thickness, but also their distance from each 

 other, and from the turning up of the lead appertaining to the gutter. The 

 two spouts were represented each by a thick wire, the shorter of which commu- 

 nicated (at the bottom) with a cistern. This cistern resting on 2 wooden pillars, 

 or posts, about one foot and a half in length at Purfleet, the same circumstances 

 and proportions were attended to, and made to correspond exactly in the model. 

 The other wire, in conformity to, and nearly in proportion with, the other 

 spout at the Board-house, descending from the gutter for about 7 inches, was 

 there bent almost at right angles, and then continued on for 12f inches, in a 

 line nearly horizontal, till it reached within 2 inches, or little more, of the 

 short wire: after which it was bent again almost at a right angle, and then 

 lengthened out to the bottom of the model, whence it communicated, by 

 another wire, with a pump or well, in another part of the house. This kind of 

 communication was necessary, because, consisting of metal, in that respect it 

 was similar to the communication at Purfleet. 



Besides the 2 cramps mentioned above, another parapet was made to put on 

 occasionally, which contained all the cramps: these were properly fixed therein, 

 and at their proper distances from each other. And the r. s. having thought 

 proper, since the accident, to order that a metallic communiaition should be 

 made between the cramps on the parapet, quite round the building, as a better 

 security from such accidents for the future, care was taken to make a similar 

 connection with the wire cramps, by means of small slips of tin-foil that were 



