326 SCIENTIFIC RECORD FOR 1884. 



fuuction of the difference between the number of cloudy and clear days 



45 

 by the formula 0=53 ^ (cloudy-clear), where n is the whole number 



of days in the period. He, however, does not recommend that we give 

 up computing mean cloudiness by taking the actual average of each 

 day's actual observation. (/>. M. Z., i, p. 341.) 



233. Roscoe and Stewart publish the results of observations made at 

 Kew, 1875-'82 on solar radiation or the heat of sunshine as registered 

 by Campbell's sunshine recorder j the original form of this apj^aratus 

 consists of a wooden block with a hemisi)herical depression into which 

 is inserted a spherical lens so that the focus of the lens lies at the sur- 

 face of the wood, and it is assumed that the sun's rays cbar or burn the 

 block in proportion to their intensity and duration. One block lasts 

 from June 21 to December 21, and is then changed for a second block 

 to last from December 21 to June 21. Twenty-four years of observations 

 seem to show that the quantity of solar heat received by the block is 

 greater from December to June than from June to December (due to 

 cloudy weather?); there is also a slight trace of a double variation in- 

 side of each sun-spot period. {Z. 0. G. M., xix, p. 546.) 



234. Prof. J. M. Pernter has made a collection of data relative to tbe 

 amount of sunshine received at different places on the northern hemi- 

 sphere, and the few stations given by him serve to increase the interest in 

 this important climatic and meteorologic element. His tables give the 

 hourly and monthly averages and totals of the amount of sunshine re- 

 corded by the Beck-Cami)bell sunshine register for five stations in Europe, 

 one in Asia, and four in Canada, all for the year 1882. [Records have 

 been maintained for a number of years with this instrument at Wash- 

 ington, but have not yet been reduced and published. In fact some 

 doubt seems to have arisen as to the value of these records.] Pernter ex- 

 presses the wish that the publication of the results of the sunshine-reg- 

 ister should be given by hours and tenths of hours, not the hourly means 

 expressed as rates per day, and not the monthly means, but the hourly 

 totals and the monthly totals. From his examination of the records 

 it seems that the depression in the curve of daily rate that had already 

 been established for Vienna at about noon appears with few exceptionsat 

 all other stations. St. Petersburg and' Winnipeg, like Vienna, show in 

 summer more sunshine in the morning than in the afternoon, and the 

 reverse in winter; all stations havemoresunshine in the afternoon than 

 morning throughout the year; this peculiarity Pernter attributes to the 

 difference between continental and marine climates. 



By making use of Schott's tables of sunrise and sunset on account 

 of their accuracy, Pernter computes the percentage of the observed to 

 the greatest possible duration of sunshine. In general the annual to- 

 tals and the annual percentages diminish with the increase of latitude; 

 the annual averages are 01 per cent, for Bola, 4(5 for Toronto, 37 for 

 ]!ila;ideburg, 47 for Wiuuii>eg, 42 for Vienna, 41 for Sydney, 71 for Alia- 



