2. “On the Moon and the Weather,” by J. S. Webb. After pointing out that observations made by the Earl of Rosse confirm
the opinion that the heat radiated from the moon has very little to do with the changes of weather, Mr. Webb proceeds to say :—The following facts, however, tend to the conclusion that the moon does exercise some influence on the weather. From observations of temperature at Greenwich, Oxford, and Berlin, it has been shown “that a maximum mean temperature occurs on the average at each of these places on the sixth and seventh day of the lunation, and a minimum mean temperature shortly after full moon.” That is to say, when the moon's surface is most heated, and the lunar radiation therefore greatest, the temperature at these places is reduced. Certain theories were based on these conclusions, which were immediately overthrown by corresponding but quite contrary facts, deduced from observations at St. Petersburg. A relation between these two sets of observations has, however, since been determined by the discovery that, at the former places, “S. and W. winds increase in frequency from new moon to the second octant, whilst in the last quarter, the same winds are at a minimum, and N. and E. winds reach their maximum.” These circumstances are sufficient to account for the variations of temperature in the south of England and at Berlin, and, from the known relations between the prevailing winds in the two regions, at St. Petersburg also. Whether there is a relation between the moon's age and these winds, or whether the observed facts are only coincidences, cannot be said to be determined. Even if we take the former view, we must remember that up to the present time this is all that has been gathered as to the direct influence of the moon on the weather, and that it does not connect any lunar phenomena with the occurrence of storms, rains, and inundations, or lead us to conclusions as to the total influence of the moon on any given day upon the weather all over the globe. Neither the effects of lunar radiation, nor the supposed atmospheric tides, if they do really exist, lend, therefore, any warrant to Lieutenant Saxby's prediction. The moon, however, may have an indirect effect on the weather in a manner which does not yet appear to have attracted the attention of meteorologists, viz., through the tides themselves. It is an ordinarily received opinion that changes of wind often take place at the time of slack water, either after the ebb or flow of the tide. With regard to particular places, this is more than an opinion—it is, I believe, a distinctly ascertained fact. On this point, however, I am speaking from memory and from personal observation; there are no registers of scientific observations to fall back upon. In Port Jackson, for instance, where there is steady fine weather with a N.E. wind blowing in from the sea, if the time of slack water after flood
tide occurs about sunset, the sea breeze dies, and a gentle air from the W. sets in. When the time of slack water is later, the N.E. wind blows far into the evening; but I do not venture to say that the changes of wind and tide always keep time with one another. I had no thought of using them for my present purpose when I made these observations. Another more important observation which I do find recorded is this :— at any given point on the coasts of Western Europe, the strongest winds and most disastrous storms come in upon the coast in the direction from which the true tide wave approaches it. The same is the case with the worst class of storms that visit our own shores, and the S.E. coast of the neighbouring continent of Australia. These come in upon us from the south-east. What I do find is that, as a rule, the most disastrous storms come in upon any coast line from the same direction as that in which the tide wave approaches it. This is a rule on the western coasts of Europe and in our own country, and on the neighbouring shores of Australia it also holds good. The worst weather on this coast and on the eastern seaboard of Australia, is that which comes in from south-east.
Mr. Bathgate said he had long thought that the hot winds experienced here were connected with those felt in Australia, and pointed out the advantage of simultaneous observations being made in the two places, in order to determine the question.
Mr. Cargill thought observations were required with regard to the effect of the N.W. wind. He was told that the wind which was dry here blew moist in the Lake district. It seemed as if the action of the heavy masses of snow about Mount Cook caused a sudden precipitation of the moisture in the atmosphere. He believed it was quite a delusion to suppose that the N.W. wind caused the swelling of the rivers by melting the snow.
The Chairman said the wind seemed analogous to the sirocco in the Mediterranean.
Mr. Gillies said Mr. Cargill's remarks about the swelling of the rivers might apply to the Waitaki and Ohau, but, speaking from personal observation, he could say that they did not apply to the Clutha and Jacob's river. Moreover, the colour of the water would always show whether a river was swollen by snow water or not. So far as regarded the southern rivers, the matter was perfectly clear, for the snow could be seen melting day by day—almost hour by hour. It was a well ascertained fact in Dunedin harbour that the wind would change with the tide.
Mr. M. Kerrow said the prevailing wind in the interior of the
province was the north-west, and it brought large bodies of rain with it. It also caused the rivers to rise. He had noticed that on the south-east and north sides of the mountains the snow line was lower than on the west side. It required a considerable amount of observation to convince him that the greater altitude of the snow line on the west side was owing to the direction of the prevailing wind. The wind had far more effect in melting snow than the sun. He had observed that the rivers rose more rapidly when a north-west wind was blowing, with a drizzling rain, than when a heavy fall of rain took place. The lakes exercised a very important influence on the discharge of our rivers, by restricting it within certain bounds. He had known the lakes to rise twelve feet. This water covered an immense area, and had it been suddenly thrown into the rivers, great mischief must have resulted. In fact, were it not for the lakes acting as reservoirs, the Clutha would spread its bed over a width of three or four miles, and do on a large scale what the Rangitata and other Canterbury rivers did on a small one.