432 Proceedings of Boyal Society of Edinburgh, [july 18, 
it was heated to 066 times. If then we divide the temperature of 
the black hall by that of the black bulb, we get a series of numbers 
inversely proportional to the cooling effect of the wind. These 
numbers are given in the sixth column. If now we multiply the 
numbers so obtained by the heating effect of the radiation on the 
black ball, we get a series of numbers representing the combined 
effects of solar radiation and wind. These numbers are given in the 
seventh column. 
It will be observed that the numbers so calculated vary with the 
errors of the Stevenson screen given in the third column, and that 
when they are divided by 10 the figures in the two columns agree 
fairly well with each other. It will, however, be noticed that the 
figures agree much better when the weather is calm and settled than 
when it is stormy. This was probably due to the fact that during 
the windy days it was also cloudy, with only short gleams of sun- 
shine, sufficient to heat up the black ball and black bulb, but not 
long enough continued to heat up the screens; or it may have been 
due to the maximum radiation temperatures not having happened 
at the same time as the maximum air temperature. The errors 
during the cloudy weather were thus probably smaller than they 
would have been if there had been continued sunshine. 
It would thus appear that, by taking observations with a black 
ball and a black bulb in vacuo, we can calculate pretty well what 
will be the excess in the readings of the Stevenson screen over those 
of the G screen. And further, a comparison of readings taken in 
this way also tells us something about the climate of the place 
which cannot be ascertained by an examination of the readings of 
the black bulb in vacuo alone. On the 24th July, for instance, the 
black bulb in vacuo was heated 69° above the temperature of the 
air, while the black ball was only heated 28°, and the error of the 
Stevenson screen was only 1°; whereas on the 18th August, when 
the black bulb in vacuo was not heated quite so much, the black 
ball had its temperature raised 42° ’5, and the error in the Stevenson 
screen was 2° *6. As the thermometer in the Stevenson screen is 
influenced very much in the same way as our bodies, by radiation 
modified by wind, we may look on the figures given in the seventh 
column of the table as representing more nearly the climatic con- 
ditions than those given by any other method at present in use. 
