68 Proceedings of the Asiatic Society. [ Marcu, 
west, causing a dispersion of air and consequent reduction of pres- 
sure, near the centre of the heated space, and a heaping up of air 
and increase of pressure at its two margins. This he believed to 
be the most likely explanation of the two maxima and the inter- 
vening minimum of pressure. At the same time he must guard 
himself by saying that the above was a very coarse and imperfect 
explanation of the phenomenon, not intended to be put forward as 
scientifically precise. As a fact the movement of the air particles 
which caused the diurnal tide of pressure was a wave movement, 
and not a real permanent movement of translation. This was 
proved by the circumstance that the tide of air pressure moved 
round the earth with the Sun and quite independent of the actual 
motion of the mass of the atmosphere at the place of observation. 
Col. 8. referred to various peculiarities in the form of the curve of 
diurnal pressure at various places, and offered comments on some 
of them. He particularly suggested the propriety of making care- 
ful observations at some small island, in an extensive sea area 
within the tropics, as a means of ascertaining the normal diurnal. 
curve in its simplest form. He noticed the well known mechanical 
law of the possible co-existence of any number of waves in a fluid 
body, and said that, no doubt, many of the local peculiarities of the 
barometrical curves, daily or other, were due to such superimposed 
waves, and that what the scientific observer had to do was to se- 
parate these and indicate their several causes. 
Col. Strachey pointed out how the diurnal variation of pressure 
was most marked when the diurnal variation of temperature was 
greatest. Also how the daily tide was best marked near the equa- 
tor, and gradually faded away towards the poles. He suggested 
as a sufficient explanation of this, that at the equator the force, 
exerted by the sun in creating the wave action in the atmosphere, 
continued constantly parallel to the actual motion of the air particles, 
forming the atmospheric wave as they revolved with the earth on 
its axis, and that consequently the impulse was accumulated in an 
intense degree, and a true accelerating force developed. As we 
leave the equator this parallelism is departed from, the actual 
direction of the air particles of the atmospheric wave being forced 
into a small circle of latitude, so that the impulse caused by the 
