70 Selim Lemström. 



PAG. 23. NOTE V. Wc niay, howcver, in thc following way, gct an idca of thc quantity 

 of lieat lost from thc uppcr parts of vegetation in a surface of earth ovcrgrown with short 

 grass. If wc place on the grass (3 cm abovc the surface of thc carth) a thcrniometcr with a 

 sphcrical bulb, so as to niakc it lie ou thc grass without touching the ground, \ve shall gct 

 (NOTE II) 



<3»= - f' pcclTdt 



p and c dcnoting thc weigh and sp. heat of thc thcrmonictcr-bulb, t, time, and dT, the con- 

 stant falling of température during thc timc dt. 



For a thermometcr of the same kind as thosc uscd at thc experiments I hâve rcccived 



or 



P'rom Curve I„ (pi. I) it is scen that thc température from 9,2.-. p. m. wheu it «as Pjio, 

 till 12,34 p. m. fcll to — 4",i2 or ö^jSS iu 3 hours and 9 minutes, from which follows 



pet = 0,0013 Cal. 



The radius of thc tlicrmomulcr bulb was 



0,444 cm. 



and, consequcutly, thc arca of thc grcat circlc, if supposcd to bc sphcric, thc bulb is cal. 



0,6193 cm^ 



In 3 hours and 9 minutes and in ni^ this makcs 



20,007 Cal. 

 and per hour and m^ 



6,485 Cal. 



This quantity of heat would bc lost, if the wholc surface werc covcrcd with a mass of mcrcury 

 within glass, correspondiug to a worth in water 



3,556 kg 



or a layer 0,3556 cm in height. If this layer of water had posscssed the eniission-powcr of 

 the thermometer-bulb, it would havc given, between 9,25 p. m. and 12,34 p. m., 6,485 Cal. per 

 hour. 



As grass, e. g. the new barleycrop, is injured only in the tips, to a lengtli of from 3 

 to 4 cm, we will assume that this crop, if eut off to 4 cm from the top and spread out 

 evenly on a surface, will take up 1 m^ with a thickness of 0,ooo5 m, and thus a volume of 



