46 REPORT — 1841. 



the fifth magnitude, with this especial object in view, has been undertaken 

 by one of the members of the Committee, conducted on the same plan, the 

 principle of which is explained in the paper alluded to. This review is al- 

 ready in a considerably advanced state, and should circumstances and weather 

 favour will i^robably be completed before the next Meeting. 



In its progress it has required the aid of skeleton charts, prepared by laying 

 down all the stars by dots from planispheres of received authenticity, and 

 sketching in the existing constellations. As the preparation of such skeletons, 

 which require to be very neatly and con-ectly executed, consumes a vast deal 

 of time and is very troublesome, they, as well as the southern charts above 

 alluded to (thirteen charts in all), have been procured to be executed by 

 Mr. Arrowsmith, which has caused an outlay to the amount of 17/. 19s. 6d., 

 leaving disposable out of the original grant the sum of 32/. Os. 6d., and which 

 the Committee consider will be required for their future proceedings. 



(Signed on the part of the Committee) J. F. W. Herschel. 



Report of a Committee appointed at the Glasgow Meeting of the British 

 Association in September 1840, for obtaining Instruments and Re- 

 gisters to record shocks of Earthquakes in Scotland and Ireland. 



It is proper to explain at the outset of this Report, that it narrates only what 

 has been done by the three individual members of the Committee resident in 

 Scotland. It was found by those members impossible to communicate with 

 their associates in Ireland in any trials for ascertaining the instruments 

 adapted to the object in view. So also, in regard to the localities in Ireland 

 and Scotland, where these instruments should be placed, no advantage was 

 anticipated from a correspondence between the members of the Committee 

 in each country respectively, as it was exclusively those connected with, and 

 resident in, the country who knevv the localities where eartliquake shocks 

 were most frequent, and where intelligent and careful observers could be 

 found. 



The members of the Committee in Scotland had several meetings in the 

 beginning of winter to consider some new forms of instruments fitted to re- 

 gister the shocks commonly felt in that part of the island. Several instru- 

 ments of different forms had previously been constructed and fixed at Comrie 

 in Perthshire, but they were found not sufficiently sensitive to indicate more 

 than a small proportion of the shocks felt in that district. 



After a good deal of consideration and a number of trials, two kinds of in- 

 struments, out of several which suggested themselves, were in the first instance 

 resolved on. The one kind was on the principle of the common pendulum, 

 the other on that of the inverted pendulum, or watchmaker's noddy. One 

 instrument was made on the first-mentioned principle, and two on the second. 

 The construction and dimensions of these will now be shortly described. 



1. Common Pendulum Seismometer. — The pendulum is thirty-nine inches 

 in length from its point of suspension to its lower extremity. At its lower 

 extremity there is a piece of soft chalk in the form of a pencil, which, as the 

 pendulum vibrates, makes a marking on a concave piece of wood painted 

 black, and forming the segment of a sphere with a radius of thirty-nine inches. 

 This segment has white circular lines painted on it parallel with its circum- 

 ference, and one inch apart from each other. It has also the cardinal points 

 of the compass marked on it. Near the lower end of the pendulum there is 

 a leaden ball of about four or five pounds weight, which is perforated through 

 the middle, so as to admit the pendulum through it. The chalk pencil 



