154 Scientific Intelligence, 



If the pupil of an eye is placed at the surface its aperture is 3 mtIi 

 it receives in each second, 



— / units of work. This quantity of work would 



1 sec h j 



require 1 year 89 days to raise 1 gram of water 1° C. A com- 

 parison of the light of the sun and that of stars of various orders 

 of magnitude is appended to the paper. — Ann. der Physik nnd 

 Chemte, 1889, No. 12, pp. 640-662. j. t. 



5. The Bolometer.— R. Von Helmholtz constructed a bolom- 

 eter of which all four branches of the Wheatstone's bridge were 

 contained in the cylindrical case of the instrument and two 

 branches of the bridge were exposed to the source of light. The 

 theory indicates that the resistance of the four equal branches of 

 the bolometer balance should be as great as possible (with suit- 

 able galvanometer resistance) that this resistance should be in the 

 form of blackened strips : that these strips should receive the 

 light along their entire length. — Beiblatter Ann. der PhysiJc, 

 1889, No. 12, p. 882. j. T. 



6. The Cavendish Mcperiment. — C. V. Boys has greatly re- 

 duced the size of the apparatus used by Cavendish to measure the 

 force of attraction between two masses. Mr. Boys shows that an 

 apparatus the size of an ordinary galvanometer can be employed. 

 As a lecture room experiment the attraction of small masses 

 can readily be shown, even though the resolved force causing 

 motiofi is no more than the -^woh'o'o °^ a degree (less than 



1^.^ of the weight of a grain), and this is possible with the 

 comparatively short period of 80 seconds. So perfectly does the 

 instrument work, that there can be no difficulty in making a 

 fairly accurate measure of the attraction between a pair of No. 5 

 or even of dust shot. — Nature, Dec. 19, 1889, p. 154. j. t. 



7. Report on the Magnetic Results of the Voyage of H. M. S. 

 Challenger. — " The voyage of the Challenger has shown that local 

 magnetic disturbance is found in the solitary islands of the seas, 

 although surrounded by apparently normal conditions similar to 

 those on the great continent. It has been suggested that the 

 magnetic portions of these islands causing the disturbance may 

 possibly have been raised to the earth's surface from the magnet- 

 ized portion of the earth forming the source of magnetism and 

 tending to prove Airy's conclusion that "the source of magnet- 

 ism lies deep. 



"In view, therefore, of past geological changes and those now in 

 progress, it may fairly be conceived, not only that larger changes 

 have likewise occurred in the distribution of the magnetic por- 

 tions of the earth appearing here and there on the surface and 

 producing local magnetic disturbance, but that there are others 

 of a more progressive character below the earth's surface which 

 are only made manifest by the secular change observed in the 

 magnetic elements. This conception with regard to secular 

 change is not intended to exclude the view that solar influences 

 may have a small share in producing the observed phenomena." — 

 Nature, Dec. 5, 1889, p. 165. j. t. 



