METEOROLOGY. 



531 





for from thirty to fifty hours in a bath of ace- 

 tate of lead at a temperature of from 95 to 

 12<r Fahr. After being thoroughly dried it is 

 in a condition for being polished with lead, tin, 

 or zinc, as may be desired, and finished with 

 a burnisher. 



METEOROLOGY. Temperature The distribu- 

 tion of heat over the surface of the earth 

 has been studied by Dr. Zenker. The amount 

 of heat that reaches the earth's surface is 

 dependent on the distance of the sun, and is 

 greater at perihelion than at aphelion in the 

 inverse ratio of the square of the sun's dis- 

 tance. The varying ellipticity in outline of the 

 earth in its various positions is not of enough 

 extent to have an influence on the amount of 

 heat received. If any one point of the earth's 

 surface is alone considered, then the heat re- 

 ceived is determined by the sine of the sun's 

 altitude or the cosine of its zenith distance. 

 From these relations it follows, leaving the air 

 out of account, that the heat received by the 

 pole on a summer day is greater than that 

 which falls on a point at the equator. Thus 

 taking as unit the heat received during twenty- 

 four hours by a place at which the sun is in 

 the zenith, the north pole receives an amount 

 of heat represented by 0-397, and a point on 

 the equator an amount represented by 0-292. 

 But the air absorbs a large part of the sun's 

 heat. The estimation of the height of the 

 atmosphere from the amount of heat absorption 

 can not be relied upon, because the chief ab- 

 sorption takes place in the deeper layers of the 

 air. For the determination of the coefficient 

 of absorption, the author accepts the values 

 obtained by Langley from his bolometric ex- 

 periments, with a reservation regarding the 

 absorption taking place in its highest layers, 

 which he does not admit. One factor of great 

 importance is the diffusion of heat, already 

 described by Clausius, from the small particles 

 of water, dust, and air in the atmosphere, 

 which are calculated under other definite as- 

 sumptions. Another factor that must not be 

 lost sight of is the reflection of heat at the 

 earth's surface. This is calculated for the three 

 cases of a surface of land, water, and snow. 

 In his calculations for the sea, Dr. Zenker 

 started with the temperature of a point on 

 its surface which was quite uninfluenced by 

 the neighboring continents, and unaffected by 

 warm or cold currents. In basing the cal- 

 culations for the land surface, the conditions 

 were first determined under which the influ- 

 ence of the neighboring sea is either noth- 

 ing or minim in amount. A region of purely 

 continental conditions was found in the neigh- 

 borhood of the east coast of Asia ; while all 

 other points were affected to a greater or less 

 extent by the neighboring sea. The observed 

 temperature on the land was therefore only 

 partly dependent upon the position of the place 

 on any given parallel, for other influences make 

 themselves felt. Hence the real and " ac- 

 cessory " temperature can be calculated for 



each parallel. The amount of heat radiated 

 from the sun, when compared with the- 

 peratures, was about the same for each 10 C. 

 of difference. Comparison of the tempera- 

 tures that really exist with those thus deduced 

 showed that the climate on the sea of the south- 

 ern hemisphere is colder than calculation would 

 make it a result attributable to the oceanic 

 currents of cold water; while, in consequence 

 of the disturbance introduced by the Gulf 

 Stream, the continental climate in the north- 

 ern hemisphere is slightly too -warm. 



Data regarding the average time of the first 

 killing frost in the United States have been 

 published in the " Monthly "Weather Review.'' 

 They were collected from four hundred and 

 thirty-two rural stations, and embody the re- 

 sults of observations ranging in duration from 

 two to forty-nine years, of which thirty-six 

 stations have records of fifteen years or more. 

 From them it appears that killing frosts oc- 

 cur throughout the year along the northern 

 border of Minnesota and Dakota. In Cali- 

 fornia they are very unusual in the eastern and 

 northeastern parts, but light frosts occasion- 

 ally occur in the western part. Hard frosts 

 come about the first of September, in the mid- 

 dle of the upper lake region ; September 15 in 

 the lower lakes and the south end of Lake 

 Michigan ; October 1 along the New England 

 sea-coast and southern Ohio ; October 15 in 

 the Carolinas ; and from November 1 to De- 

 cember 15 in the States farther south, to cen- 

 tral Florida. The observations involve an 

 average error of about eighteen days ; and will 

 therefore have to be continued through many 

 years to obtain an approach to reasonable ac- 

 curacy in fixing the date. 



According to Yon Tillo's " Researches upon 

 the Distribution of Air-Pressure and Tempera- 

 ture over the Earth," the mean temperatures, 

 centigrade, of the continents are as follow : 



The mean of the air-pressure of the whole 

 northern hemisphere is. in January, 761*7 mm. } 

 in July, 758-5 mm.; or about 3-2 mm. 

 The corresponding values for temperature are 

 8-3 and 22-6 ; difference, 14-3 ; so that a 

 change of 1 mm. in pressure is equivalent to 

 one of 4'5 a in temperature. 



The greatest winter cold known to exist upon 

 the globe prevails at Werkojansk, in Siberia, 

 which is situated in the valley of the Jana, 

 about nine feet above the level of the river, in 

 latitude 67 34' X.. longitude 133 51' E., and at 

 a height of about 350 feet above the 

 Monthly means of 58 Fahr. occur in Decem- 

 ber, and minima of 76 are usual for the three 

 winter months, December to February. In 



