ON THE EXPLORATION OF THE CAVES OF THE SOUTH OF IRELAND. 209 



On July 19, before seeing the Kew horizontal force curves, I wrote as 

 follows : / am led to conjecture that at 8.45 p.m. on the 29th, and at 11.15 

 p.m., there is an increase in the horizontal force. 



On comparing the Kew horizontal force curves I find that from 8.45 

 to 9.5 p.m. the horizontal force is inci'easing rapidly, and that it decreases 

 again from 9.5 to 9.30 p.m. At 10.40 the horizontal force again increases, 

 and after a slight decrease about 11 o'clock, there is again an increase in 

 the horizontal force, beginning at 11.15 p.m., and ending at 11.30 p.m., 

 i.e., when the St. Petersburg declination needle reaches its greatest 

 ■westerly deviation. 



On comparing an exceedingly good photograph from Vienna for March 

 26-27, with the photograph from Kew, which is also good, in a disturbance 

 lasting from 5 p.m. to 7 p.m., in which there were twelve distinct deflec- 

 tions in each direction and a decided character given to the curve, but in 

 which no excursion was as great as 2' from the mean position, I fovmd 

 that the curves were absolutely coincident. 



The Stonyhurst positives agreed with Kew as far as one could judge, 

 but the agreements between the Kew and Vienna curves here spoken of 

 are such as are entirely beyond the power of testing by a positive. Almost 

 the whole of the Vienna photograph of the disturbance lies within the 

 breadth of the base line in the Stonyhurst positive. The oscillations are 

 also found to take place absolutely at the same instant of time at Kew 

 and at Vienna. Similar instances occur on March 31 between 12 and 

 1 p.m. and between 6 and 7 p.m. 



The St. Petersburg tracings also show the same disturbances occurring 

 at the same times, but the agreement of these Vienna and Kew 

 curves is far greater than any that can be tested by means of tracings ; at 

 the same time, there are numberless instances of comparison which might 

 be given which .show that the St. Petersburg tracings are remarkably 

 good. They are also taken on a very excellent tracing paper, and the 

 hours are carefully marked on the curves, so that there is no difficulty in 

 arriving at the time at which any given disturbance occurs. 



Tt would be easier to make accurate measurements of time if the base 

 line were nearer to the curve than it is in the Vienna photographs, and if 

 only one curve were photographed on each slip at all stations, as is the 

 case in the Vienna photographs. For the comparison of magnetic dis- 

 turbances it is important that the arrangement of lamps, lenses, &c., 

 should be as exactly as possible the same at all stations, for the accuracy 

 of the agreement of the results is such that any variation in this arrange- 

 ment interferes with the degree of accuracy of the conclusions which may 

 be drawn as to the character or the cause of magnetic disturbances. 



\ 



First Re.port of the Gonnyiittee, consisting of Professor A. Leith 

 Adams, the Eev. Professor Haughton, Professor W. Boyd Dawkins, 

 and Dr. John Evans, appointed for the purpose of exploring the 

 Caves of the South of Ireland. 



The following is a preliminary Report on the Bone Caverns, near Middle- 

 ton, in the county of Cork, lately explored, in part, by R. J. Ussher 

 and J. J. Smvth, Esqrs. The work has been restricted to a few days' 



1880. ' p 



