18 NOTES BY THE EDITOR 



mosphere must set some limit to the magnifying power of our tele- 

 scopes. In a variable climate, indeed, the vapors and local changes 

 of temperature, and consequent inequalities of refraction, offer Carious 

 obstructions to astronomical research. But we must meet t")e diffi- 

 culty in the only way in which it can be met. The astronomer can 

 not summon the zephyrs to give him a cloudless sky, nor ccmmand a 

 thunder-storm to clear it. He must transport his telescope to the 

 purer air of Egypt or India, or climb the flanks of the Himalaya or 

 the Andes, to erect his watch-tower above the grosser regions of the 

 atmosphere. In some of those brief yet lucid intervals, when distant 

 objects present themselves in sharp outline and minute detail, discov- 

 eries of the highest value might be grasped by the lynx-eyed astron- 

 omer. The resolution of a nebula the bisection of a double star 

 the detection of the smaller planetary fragments; the details of a 

 planet's ring the evanescent markings on its disc the physical 

 changes on its surface, and perchance the display of some of the dark 

 worlds of Bessel, might be the revelations of a iroment, and would 

 amply repay in national glory the transportation of a huge telescope 

 to the shoulder or to the summit of a lofty mountain." 



The result of the experiments recently made by Professor Airy of 

 the Greenwich Observatory, in one of the deepest of the English coal- 

 pits, for ascertaining the variation of gravity at great depths, have 

 proved beyond doubt that the attraction of gravitation is increased at 

 the depth of 1260 feet by T g-^oo- P art - 



During the past year, another very important astronomical work 

 has been performed, by which the difference of longitude between 

 Paris and Greenwich has been ascertained. The number of days con- 

 sidered available for longitude, in consequence of transits of stars 

 having been observed at both Observatories, was 12 ; and the num- 

 ber of signals was 1,703. Very great care was taken on both sides 

 for the adjustment of the instruments. The resulting difference of 

 longitude, 9' 20" -63, is probably very accurate. It is less by nearly 

 V of time than that determined in 1825 by rocket signals under the 

 superintendence of Sir John Herschel and Colonel Sabine. The time 

 occupied by the passage of the galvanic current appeared to be one- 

 twelfth of a second. 



In his annual Report, the English astronomer royal regrets that, 

 while the Greenwich astronomical observations have assumed such a 

 shape that the astronomer will find all the moving bodies of the solar 

 system presented in the utmost extent and accuracy, the same asser- 

 tion can not be applied to the magnetical and meteorological observa- 

 tions ; not, however, from any defect in the instruments or observations; 

 for these have acquired an extraordinary excellence and precision, par- 

 ticularly in the photographic branch of rogistration. ''But, 11 to use the 



