112 Temperature at Stockholm. [Feb. 



As fresh broken specimens of this mineral look as if they were 

 spotted with coagulated blood, I have given it the name of 



lythrodes (from to Xv9pov). 



Some of the varieties of this mineral, where two of the plates 

 that occasion the concealed foliated fracture are set perpendicu- 

 larly upon each other, may be mistaken for a species of felspar ; 

 but a closer iu^^pection, together with the consideration of its 

 consthuents, will undeceive us. When lythrodes exhibit^ sinall 

 splende'it particles, it for tains lahrad-re felspar mixfd with it. 

 The other sui>stances occasiona!!}' mixed with this mineral are 

 black hornblende, white analcinie, and dark brown zircon. 



— — — . — . — ,, M ., ^ 



Article IV. 



On ike Difference of Temperature^ during a period of 50 years^ 

 at Stockholm, according to OOiervatioiLs made ai the Observa- 

 tory of the Academy of Sciences, By J. ofverbom.* 



The process by means of which the sun's rays communicate 

 heat to our earth will probably continue long unknown. Not- 

 withstanding the attempts of Bouguer and Lambert the doctrine 

 that their greater or smaller intensity depends upon their angle 

 of incidence, and upon the greater or smaller portion of the 

 atmosphere through which they pass, seems still to prevail. 

 Experience shows us that the sun produces the greater quantity 

 of heat the more highly he is elevated ; but at the same time 

 that the heat is greater, a preceding day acquires the power of 

 leaving an excess upon the following day. What confirms this 

 proposition is, that the greatest heat does not happen at the 

 summer solstice, but sometimes more than a month after it ; 

 just as the greatest heat of the day happens a little after two 

 o'clock. 



The changes in the winds and the thickness of the atmos- 

 phere, together with the variations of the barometer and 

 hygrometer, and probably many other circumstances not yet 

 understood, occasion the heat of one year to differ from that of 

 another, even though the observations be made at the same time 

 of the day, and be kept regularly during the whole year. But 

 as the power of the sun ought to be the same every year, one 

 may hope that by taking a great many years together their 

 differences and anomalies vv^ill be sunk in each other, and the 



* From Kongl. Vetecskaps AcadenaicKS rtya Hacidlingar, torn. 29, p. 294, 



for r.iOS. 



