130 
while the water below supplies some of the heat rendered 
latent by the evaporation of the water, the air above it 
supplies its share, and is cooled. In both cases the heat 
thus lost is made good by the direct radiation from the 
sun. Through a moderately dry atmosphere the rays 
ass with comparatively little heating effect, but are 
argely absorbed on entering the water. Consequently 
the loss of heat which the water suffers by evaporation at 
the surface of separation is made good more abundantly 
than that sustained by the air; and the difference in 
power of absorption of radiant heat exhibited by these 
two substances is thus sufficient to keep up a permanent 
difference of temperature between the water and the air 
immediately above it. 
Starting with air and water at the same temperature, 
Wwe may imagine the process taking place in three acts. 
First, the water at the surface evaporates, and the air 
on the one side, and the water on the other, are cooled ; 
second, in order to make up for the heat thus rendered 
Jatent and lost, the sun shines upon both alike, but the 
water absorbs a larger proportion of the heat of its rays 
than the air does; and finally, a portion of this excess 
is then removed from the water by the simple contact of 
the air at its surface. The nett effect of these causes is 
to produce a permanent excess of temperature of the 
surface-water of the sea over that of the air above it, 
provided that that air is not completely saturated with 
moisture, 
From what I have seen and experienced in the regions 
visited by the south-west monsoon in the east, I cannot 
doubt that there are often cases where the most carefully 
exposed wet- and dry-bulb thermometers would show 
identical readings, and the atmosphere is completely 
saturated with vapour of water. Thus it is probable that 
the temperature of the air would not be inferior to that of 
the water. Further, when, on the eastern coasts of Asia, 
the south-west monsoon blows out of the China Sea and 
penetrates far into the North Pacific, off the coasts of 
Japan it attains a latitude of naturally lower temperature 
than that from which it proceeded, so that much of the 
water with which it was laden, and which is held 
diffused through it as a mere gas, is condensed and re- 
mains suspended in it, producing a visible haze, which 
obscures the horizon and condenses on all solid objects 
exposed to it. Here the conditions are reversed, and 
instead of the air losing heat to evaporate the water, it 
receives the heat liberated by the condensation of the 
steam removed from waters of lower latitudes. Such 
conditions are, however, certainly exceptional, and there 
can be little doubt that, as a rule, the temperature of the 
surface-water of the sea is higher than that of the air. 
The temperature of the air depends on that of the water 
which tends to warm it and the degree of its own dryness, 
by virtue of which the water has a tendency to evaporate 
into it and, by extracting heat from it for this purpose, to 
cool it. 
It is obvious that local circumstances such as currents 
may produce differences between the temperature of the 
air and the water, but such cases are not here under 
consideration. J. Y. BUCHANAN 
Mendoza, March 18 
THE REV. T. W. WEBB 
Y the death of the Rev. Thomas William Webb, M.A., 
F.R.A.S., English astronomy has lost one of its most 
assiduous and accomplished votaries. Mr. Webb, who 
had reached the age of 79 years, passed a long life as the 
incumbent of two obscure Welsh livings, held by him in 
succession. At Tretire he may be said to have laid the 
foundations of those astronomical tastes which took their 
finished and best-known shape during the later years of 
NATURE 
| 
[ Yune 11, 1885 
his life whilst he was incumbent of Hardwick, in Brecon- 
shire. He was a genial and right-thinking parish priest, 
whose highest aim was the performance of his duty. For 
the sake of astronomy it was well perhaps that he obtained 
so little ecclesiastical advancement ; for had things been 
otherwise it is probable that he would never have deve- 
loped those scientific tastes which have made his name 
almost a household word. It was my privilege to make 
his acquaintance upwards of twenty years ago, and I look 
back with extreme pleasure to the many letters which have 
passed between us on practical matters connected with 
observational astronomy and the use of instruments. 
Whilst Mr. Webb in bygone years used to write a good 
deal in the current scientific magazines of the day, especi- 
ally the Zrtellectual Observer and the Student, it was by 
his “ Celestial Objects for Common Telescopes” that he 
became chiefly known in the astronomical world. This 
work, published in the year 1859, was designed to be a 
cheap popular abridgment ina modified form of Admiral 
Smyth’s “Celestial Cycle,’ which had done right good 
service in providing English amateurs with information as 
to what to look for and how to find. By 1859 Smyth’s work 
had become both out of print and somewhat out of date, 
and Mr. Webb’s unpretending abridgment filled at once 
an undoubted void. It is indeed not wholly correct to 
speak of Webb’s “ Celestial Objects”? as an abridgment 
of Smyth’s older, larger, and more expensive volume. It 
was this; but it was also a good deal more, for 
whilst it offered to the possessors of small telescopes 
convenient lists of objects deserving of their attention, it 
also supplied an enormous amount of original information 
connected with the sun, moon, and planets, and the use of 
telescopes. ‘This information, though no doubt suggested 
by Admiral Smyth’s style, was no mere vechauffé of other 
people’s work, but represented the personal experience of 
an intensely industrious and persevering man working 
under great difficulties through lack of instrumental 
means. 
I shall never forget the feeling of blank astonishment 
which crept over my mind one day when (in, I think, the 
year 1864) Mr. Webb told me that the first edition of his 
book, and all his magazine articles up to that date de- 
scribing double stars and clusters, were founded on studies 
pursued by means of a telescope set up in his garden and 
not equatorially mounted, This, I well remember, was 
not said in any spirit of boasting in the garb of mock 
modesty, but was the casual utterance of a simple truth 
disclosed without effort or intention. I do not think 
I ever came in the way of any student of nature of 
whom it could be so truly said that he was “ without 
guile.” 
Mr. Webb was every inch a gentleman, and a philosopher 
in the highest sense of the word. Every line that he 
wrote contained either the record of some fact noticed by 
himself, or a sensible deduction from some other facts. 
When his facts had come to an end his pen ceased to pass 
over paper, and the result was that no one ever read a 
sentence written by him without learning something useful, 
set forth in the fewest possible words, often, indeed, in a 
form of concentration which erred on the side of incon- 
venient brevity ; but in these days of penny-a-lining (and 
it may even be admitted that there is even such a thing 
as science penny-a-lining) Mr. Webb’s habitual terseness 
cannot be described as a vice. His private letters show 
that, where necessary for the instruction of a young 
astronomer, he never grudged time and trouble for going 
into details. The highest praise that can be awarded him 
is that he not only did many usetul things himself, but 
that he set an example of patient and industrious research 
which resulted in many young men all over the British 
Empire seeking to imitate his cheery and sensible style 
of work and thought. ; 
G. F. CHAMBERS 
a 
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