12(; MESSES. M-. N. SHA^V AND AV. ?T. DINES: METEOEOLOGICAL OBSERVATIONS 
The lieights, as read on tlie trace, corresponded witli the computed heights within 
about 5 per cent, until July 23, wlien tlie instrument fell into the sea. Upon its 
recovery it continued to give satisfactory curves, hut direct observations of height 
sliowed that the scale-value had become altered, and from tliat date a correction of 
15 per cent, was applied to the readings of height on account of the change of scale- 
value, tlie jiercentage being determined from obseinuitions of height in the manner 
described. With these corrections the determination of lieights reached an accuracy 
of about 5 per cent. 
The estimate of the humidity depends on the extension or contraction of a bundle 
of hairs. Very accurate results are certainly not obtainable in this way when the 
hygrometer is used over the sea, and it is doubtful whether they are in any case. In 
rough weather the spray Hew over the tug, the hairs were at times wetted with salt 
water ; then also during rain, and when the kite was in a cloud, they were actually 
covered with drops of water. Tlie charts frequently show tlie condition of over¬ 
saturation, and all that could be done was to set the pen frequently by the screw 
provided for the purpose, so that in saturated air it should indicate a humidity of 100. 
In spite of these disadvantages, the hygrometer retained its sensitiveness during 
the ascents, but it was felt that no great degree of accuracy could be attributed to 
the readings, and on that account, in dealing with the results, only four stages of 
humidity have been used, viz. :—Very dry (V.D.), under 60 per cent. ; dry (D.), from 
60 per cent, to 80 per cent. ; moist (M.), from 80 per cent, to 05 per cent. ; and 
saturated (S.), above 95 per cent. 
Anothei' question that requires consideration is the relation between the temperature 
and humidity of the instrument and the temperature and humidity of the air wliich 
surrounds it. The current of air whicli supports the kite, whether due to wind or 
the motion of the vessel carrying the apparatus, must in any case be considerable, and 
under ordinary conditions the whole instrument may be supposed to take up I'apidly 
the temperature of the air current within narrow limits of accuracy, but in the 
moist atmosphere which is generally to be found not far from the surface of the 
coasts of the British Isles a special difficulty arises. The temperature of the air, and, 
in consecpience, that of the instrument, decreases as greater heights are reached, and 
increases during the descent. In descending, the instrument is therefore exposed to 
successive layers of air warmer tlian itself, at the same time the humidity not 
infrequently increases during the descent, and some condensation of water from the 
moist air may result if the change of height is rapid. Such condensation would be 
slight, and perhaps with sufficiently slow descent its ellect might l^e neglected. In 
the actual experiments a good deal of water was certainly found occasionally in tlie 
wire during the winding in. Sometimes a constant drip took place from a piece of 
cotton waste placed on the wire to prevent the water reaching the reel of wire. This 
was attributed to drops of water collected by the wire from clouds and not to 
condensation. Water would be collected in a similar manner by the exposed parts of 
