APPENDIX. 



95 



cylinder intended to stand on it ; for the larger sizes they may he discs of ahout 

 2 inches in thickness, to he firmly fixed to the ground by long spikes driven through 

 them ; while for the smaller cylinders they may be rods of about a foot long, pointed 

 at one end, and driven into the ground. The cylinders should be arranged as 

 below : — 



By this arrangement a clear space of 18 inches can he left between each pair of 

 cylinders and a clear margin of 3 feet ronnd the ontside of the group. The stands 

 being all fixed in position, and all projecting the same distance above the previously 

 levelled ground, and dry sand filled in up to the level of the tops of the stands, 

 nothing now remains but to place the cylinders each on its respective stand and 

 await the arrival of an earthquake. 



To use this instrument, it will he necessary to have some means of reading off 

 the exact direction in which the cylinders are overthrown ; and for this nothing could 

 be more convenient than a compass with a swinging card, mounted in a square wooden 

 box ; the edges of this box should be square to each other, and on the side of the 

 circular well in which the card works there should he a vertical mark so placed that 

 a line drawn through it and the point of suspension of the card will he parallel to 

 two of the sides of the box ; then by simply placing one of these against the over- 

 thrown cylinder, the mark will coincide with the exact direction in which the cylinder 

 has fallen. If such a compass is not obtainable, one with an ordinary needle will do, 

 using it in the same way as before, and remembering that whatever number of degrees 

 the needle may stand over, the true direction is that number of degrees on the opposite 

 side of north ; thus, if the needle stands over north 50° east, the direction in which the 

 cylinder has fallen is north 50° west. It will be well to add here that the readings 

 should always be taken in degrees east or west of north ; such phrases as north-west 

 or south-south-east are far too vague. 



Observations taken by this instrument should he entered in a regular form in a 

 special book. The first page should be occupied by details of the number of cylinders, 



( 95 ) 



