ON THE GRASS AND AT SIX FEET FROM GROUND. 143 



meteorological purposes, and as no better position could 

 be found for the solar-radiation thermometer than on the 

 apex of the roof of the shade-stand, which is six feet from 

 the ground, I fixed a similar thermometer in a similar 

 position at Eccles, in order that I might institute a com- 

 parison of solar radiation between Eccles and the Borough. 

 Though I anticipated very different results from a ther- 

 mometer thus placed than I had found from a similar 

 thermometer placed upon the grass, I was not prepared to 

 find them so widely difl^erent as I shall here present them. 

 The instruments used are the ordinary exposed black-bulb 

 self-registering thermometers duly compared. I have also 

 added a column of comparison from results obtained by a 

 self-registering black-bulb thermometer placed in vacuo 

 on the grass. The observations are for the month of 

 October ohly, the only complete month in which all the 

 instruments have been used. 



It appears therefore that for the month, at a position 

 six feet above the ground, there is a mean diftereuce of 

 solar influence of nearly 4 degrees above that upon the 

 grass ; and in some extreme instances the difference has 

 been from 10 to nearly 12 degrees. A thermometer placed 

 in vacuo on the grass has only exceeded this difference by 

 I '7 degree. These results show how important it is that 

 some definite principle should be adopted in the placing of 

 solar thermometers, as certainly no comparison can be 

 made between the amount of solar radiation at any two or 

 more places, unless some common plan of placing the in- 

 struments be adopted. 



