December, 1905.J 



KNOWLEDGE & SCIENTIFIC NEWS. 



297 



the platinum tip of the rod B passes exactly through 

 Its centre. Thus, as both the rod B and the hole in 

 the plate G are subject to displacement, and as the rods 



Fig. 4.— Agamennone's Seismoscope. 



B and C have different rates of \ ibration, it is obvious 

 that a very small movement of the ground is sufficient 

 to bring the tip of the rod B into contact with the rim 

 of the hole in the plate G. 



This forms the essential part of the apparatus, but 

 several details are required in order to adjust the tip 

 of the rod centrally within the hole. In the earlier 

 forms of the appiu-alus, the plate G was attached to an 

 arm springing Irom the rod C, and provided with two 

 screws at right angles to one another for making the 

 necessary adjustment. But, as the rod C vibrates 

 more rapidly than the rod B, it was found advisable to 

 transfer the adjusting apparatus to the latter. The 

 thick steel wire, which forms the lower part of the rod 

 B, is fixed to the bottom of a strong tube of brass H, 

 let into the base A. At the top, this tube ends in a 

 brass rmg, in which work two screws S and S, at right 

 angles to one another, which press against the thick 

 steel wire forming the lower portion of the rod B. 

 With this change, tlie necessary adjustments are made 

 more easily than in the earlier forms of the instrument ; 

 but, to attain this end still more rapidly, tlie stout rod 

 D is provided, by touching which the oscillations are 

 quickly damped. 



The two rods B and C are electrically insulated by 

 discs of ebonite from the base of the apparatus, and 

 are connected with the binding screws K and L, and 

 these again with the binding screws of the seismoscope 

 clock. This is an ordinary clock, the pendulum of 

 which is drawn to one side and held back by a small 

 tooth at one end of a lever. Immediately the platinum 

 tip of tlie rod B touches the rim of the hole in the plate 

 G, the circuit is completed, an electro-magnet fixed to 

 the base of the clock raises the toothed end of the lever, 

 and the pendulum is thus released. If the clock is pre- 

 viously set at some known time, say twelve, the time 

 indicated by the clock when next observed gives the 

 time that has elapsed since the beginning of the shock. 

 If an electric bell is included in the circuit, attention 

 may be drawn to the fact tliat the pendulum requires 

 re-setting ; but it would be more satisfactory if the 

 record were made, as in Professor Marvin's seismo- 

 scope, on a revolving drum, the rate of vihich is not 

 interfered with by any but a very strong shock. 



On account of the delicacy of Dr. Agamennone's 

 seismoscope, it is necessary to exercise some care in 

 the choice of a site. It should be placed at least in a 

 room on the ground floor, but better still in a cellar at 

 some distance from a frequented street. The most 

 satisfactory foundation would be one of stone- sunk in 

 the ground below and entirely disconnected from the 

 cellar floor. It should also be covered by a glass shade, 

 in order to protect it from currents of air or other 

 accidents. 



Photograph of the Svirv. 



October 22nd. 1905. 



The accompanying photograph was taken with an 

 ordinary 4|-inch astronomical refractor telescope. It 

 is enlarged three diameters from the original negative, 

 which was obtained with a power of 40 on the telescope. 

 A yellow isochromatic screen was used, and the ex- 

 posure rirodth second on a Cadett lantern plate. The 

 photograph shows the large group of spots (which was 

 visible to the naked eye in October) nearing the sun's 

 western limb, and another large spot surrounded by 

 faculee just coming into sight on the eastern limb. The 

 photograph was taken by Mr. E. W. Barlow, F.R.A.S., 

 of Bournemouth. 



