58 Proceedings of Royal Society of Edinburgh, [jan. 17 , 
long and 7 mm. in diameter. It has therefore a greater inertia than 
the other. A and B are the curves of temperature for two Steven- 
son screens, one with the bottom open and the other with it closed; 
while C is the curve of temperature given by the new screen 
presently to be described. The temperatures shown in fig. 2 were 
taken on the 18th October. There were a few passing clouds at 
the time, and a strongish north-east wind was blowing. The readings 
were taken simultaneously by two observers, at intervals of one 
minute from 11 ’59 to 12 ’20, when they were stopped on account 
of the radiation effect falling to zero, and all the different ther- 
mometers reading nearly alike. 
It will be seen from an examination of the curves that the fine- 
bulbed thermometer moved much more rapidly than any of the 
others. This is not shown so well in the curves as it might be, 
as the interval of one minute is much too large to show the fluctu- 
ation of this instrument, for in the interval between two observations 
it often indicated temperature much above or below the recorded 
readings. In the first rise of the curves from 12 to 12.2, there 
is no very great difference in their steepness. This is probably 
due to no observations being taken at 12.1; but take the rise 
beginning at 12.4, and here the effect of the inertia of the 
different arrangements is very marked. From 12.4 to 12.5 the 
fine-bulbed thermometer rose 0°‘8, and the large bulb 0°*3, while 
the screens only rose about 0°T. During the next minute the rate 
of increase of temperature of the fine bulb greatly diminished, as it 
was near the temperature of the air, while the rate of the others 
increased. It will be noticed that the two exposed bulbs FB and 
LB arrived at their maximum and began to fall before the screens 
A and B got to their maxima, and so long as the fall continued 
they kept falling in advance of the others, In the rapid fall which 
began at 12.11, in one minute the fine bulb fell 0°'9, the large one 
0 o, 7 ; while the screens A and B fell only about 0 o, 3, and they took 
four minutes to fall the 0 o, 9 lost by the fine bulb in one minute. 
One effect of this is that while the fine bulb, if read at very short 
intervals, would give a curve like the edge of a saw, with irregular 
teeth set at intervals of less than one minute, the inertia of the 
screens causes them to smooth over these irregularities, and to give 
a curve with fewer and less abrupt changes. 
