2l8 
[April, 
The Radiograph and its Uses. 
curiously exemplified in the photophone. Prof. Bell, indeed, 
has played the part of a god, for has he not inspired a ray 
of light ? Great as his invention is, however, it is probably 
but the stepping-stone to one still greater which is to come, 
namely, the transmission of light itself by means of elec- 
tricity. 
For the illustrations to the above article we are indebted 
to the courtesy of the publisher of the “ Engineer.” 
IV. THE RADIOGRAPH AND ITS USES. 
§ N important step has just been taken in the difficult 
science of Meteorology. Before the final goal of 
prevision could even be conceived of as attainable, 
it was necessary that all those points which distinguish be- 
tween season and season, and between climate and climate, 
should be regularly observed and put on record. In this 
direction wonderful advances have been made. We note the 
daily rainfall, the direction and the velocity or pressure of 
the wind, the degree of atmospheric moisture, and the max- 
imum, minimum, and mean temperature. But as regards 
this last item, temperature, there was till very lately a great 
deficiency in our observations, all self-registering thermo- 
meters notwithstanding. Suppose that on the 13th of 
August last a certain temperature was observed. Was this 
degree of heat due to the adtion of clear sunshine, or to a 
current of warm air though the sky was overcast, or to a 
combination of the two agencies ? It will easily be seen 
that this question is of moment, since the two kinds of heat 
differ in their adtion upon vegetable and animal life. 1 hus 
bright sunshine is necessary for developing the flavour of 
fruits and the aroma of flowers, and for ripening the grain, 
whilst warm air, unaccompanied by diredt sunlight, is desired 
for the germination of seeds and the earlier growth of plants. 
Hence if our meteorology is to explain why certain crops 
succeed better in one summer than in another, and in 
France or America better than in England, it must be pre- 
pared to show which of these two sources of heat plays in 
such season or country the more prominent part. 
It will be seen that, in registering the amount of diredt 
solar adtion at any place, there are two variable quantities to 
be regarded whose produdt yields the total sought. There 
