20 Tfie Astronomer-Royal on the [Feb. 2, 



matter in the internal mass ; from which the proportion of density 

 is at once found. Moreover, it appeared probable, upon estimating 

 the errors to which observations are liable, that the resulting error 

 in the density, in this form of experiment, would be less than in the 

 others. 



Accordingly, in 1826, the speaker, with the assistance of his 

 friend Mr. Whewell (now Dr. Whewell), undertook a series of expe- 

 riments at the depth of nearly 1200 feet, in theDolcoath mine, near 

 Camborne, in Cornwall. The comparison of the upper and lower 

 clocks (to which further allusion will be made) was soon found to 

 be the most serious difficulty. The personal labour was also very 

 great. They had, however, made a certain progress when, on rais- 

 ing a part of the instruments, the straw packing took fire — (the 

 origin of the fire is still unknown), — and partly by burning, and 

 partly by falling, the instruments were nearly destroyed. 



In 1828 the same party, with the assistance of Mr. Sheepshanks 

 and other friends, repeated the experiment in the same place. 

 After mastering several difficulties, they were stopped by a slip 

 of the solid rock of the mine, which deranged the pumps and 

 finally flooded the lower station. 



The matter rested for nearly twenty-six years, the principal 

 progress in the subjects related to it being the correction to the 

 computation of " buoyancy " of the pendulum, determined by 

 Colonel Sabine's experiments. But in the spring of 1854, the 

 manipulation of galvanic signals had become familiar to the As- 

 tronomer Royal, and the Assistants of the Greenwich Observatory, 

 and it soon occurred to him that one of the most annoying diffi- 

 culties in the former experiment might be considered as being 

 practically overcome, inasmuch as the upper and lower clocks could 

 be compared by simultaneous galvanic signals. Inquiries, made in 

 the summer, induced him to fix on the Harton colliery near South 

 Shields, where a reputed depth of 1260 feet could be obtained ; 

 and as soon as this selection was known, every possible facility and 

 assistance were given by the owners of the mine. Arrangements 

 were made for preparing an expedition on a scale sufficient to over- 

 come all anticipated difficulties. A considerable part of the ex- 

 pense was met by a grant from the Board of Admiralty. The 

 Electric Telegraph Company, with great liberality, contributed 

 (unsolicited) the skill and labour required in the galvanic mount- 

 ings. The principal instruments were lent by the Royal Society. 

 Two observers were furnished by the Royal Observatory, one by 

 the Durham Observatory, one by the Oxford Observatory, one by 

 the Cambridge Observatory, and one by the private observatory of 

 Red Hill (Mr. Carrington's). Mr. Dunkin, of the Royal Observa- 

 tory, had the immediate superintendence of the observations. 



The two stations selected were exactly in the same vertical, ex- 

 cellently walled, floored, and ceiled ; the lower station, in particular, 

 was a most comfortable room or rather suite of rooms. Every 



