390 SCIENTIFIC RECORD FOR 1885. 



Stars in the Durcbmusterung, that upon the meteoric theory of the zo- 

 diacal light it is to be expected that a continuous zodiacal band should 

 be present; but the question of its actual visibility is complicated by 

 the slight maxima of stellar density which are situated along those 

 parts of the ecliptic most readily accessible to observation from stations 

 in the northern hemisphere. An interesting result is obtained from 

 an examination of the elements of the 237 asteroids first discovered, 

 from which it would seem that the belt of sky occupied by the projec- 

 tions of the orbits of these asteroids " presents certain peculiarities 

 which correspond to those of the zodiacal light, and suggest the hy- 

 pothesis that the light may be partly' due to minute objects circulating 

 in orbits like those of the smaller planets." (Nature.) 



THE SUN. 



Langley^s researches on solar heat. — "The results of the work upon 

 which Professor Langley has been engaged for the last several years 

 have recently been published in a complete form as Volume xv of tiie 

 Professional Papers of the United States Signal Service. No work 

 more thoroughly aggressive, more calculated to further the i^rogress of 

 science and to render it secure, has been undertaken during late years 

 than that which Professor Langley has carried out, chiefly by means 

 of his ingenious and useful instrument, the bolometer. - - - The 

 first chapter contains the ijreliminary observations made at Allegheny, 

 from which Professor Langley deduced the value of the solar constant 

 as 2-84 calories, a much larger quantity than that generally accepted 

 hitherto. The observations also showed him that, contrary to the gener- 

 ally received opinion, absorption occurred in the visible portion of the 

 spectrum, i)articularly in the green and blue, and that it diminished as 

 the extreme infra-red was approached, and convinced him that the labor 

 and expense involved in repeating the observations at the base and at 

 the summit of a lofty mountain would be well repaid by the gain in 

 our knowledge. 



" In July, 1881, therefore, Professor Langley started for Mount Wliit- 

 ney, a lofty eminence in the Sierra i^evada of Southern California, 

 over 14,000 feet in height, which seemed to combine all the needed re- 

 (juiremeuts. The second chapter gives an interesting account of the 

 journey to Mount Whitney. Then follow several chapters of results of 

 observations and descriptions of the instruments used. Amongst these 

 were a water pyrheliometer after Pouillet's model, a mercury pyrhe- 

 liometer, two globe actinometers, a 'solar comparator,' and the spectro- 

 bolometer. In Chapter xiv the amount of the atmospheric absorption 

 is shown to be about 40 per cent., or double that usually supposed. 

 Then follow chapters on ' Sky Radiation,' ']!^octurnal Eadiation,' &c. 

 Chapter xxi gives a general summary of the results ; and the most 

 l)robable value of the ' solar constant ' is given as .3 calories. Three appen- 

 dices follow, on the reduction of psychroraeter observations, the deter- 



