The scope of this paper precludes us from entering into the complicated question of the non-cyclonic rainfalls in this country. It will be enough to state that the prognostics which precede them are rather those associated with broken weather, such as bright sunrises or heavy clouds banking up without the barometer falling, than the muggy, dirty weather of a cyclone front. The warning they give is also much shorter, rarely more than three or four hours, if so long.
The result of this paper may be summarized as follows:
The authors explain over one hundred prognostics by showing that they make their appearance in definite positions relative to the areas of high and low atmospheric pressure shown in synoptic charts. The method adopted not only explains many that have not hitherto been accounted for, but enables the failure as well as the success of any prognostic to be traced by following the history of the weather of the day on a synoptic chart. The forms discussed are cyclones, anticyclones, wedge-shaped and straight isobars. The details of weather in the last two are now described for the first time. They also point out that prognostics will never be superseded for use at sea and other solitary situations, and that prognostics can be usefully combined with charts in synoptic forecasting, especially in certain classes of showers and thunder-storms which do not affect the readings of the barometer.[[1]]
DISCUSSION.
Dr. Tripe said that some of the Fellows might think the paper hardly suitable for reading at a meeting or printing in the journal of a scientific society, but many of them took an interest in such papers, because they were comparatively simple. In reference to the table of solar and lunar halos in connection with rainfall, it appeared that rain was pretty sure to fall within three days after the occurrence of a lunar halo, and to the extent of 80 per cent., as regards solar halos, on the first or second day.[[2]] He considered visibility was a good prognostic, and afforded a more certain indication of the speedy occurrence of rain than even mare’s tails. What caused visibility was unknown to him. The prediction of rain from damp walls depended chiefly on the previous weather; a sudden change from cold to warm would have the effect of making walls condense the moisture contained in the air without approaching rain. The falling of soot down a chimney was, he thought, hardly a good prognostic; it was caused to a great extent by the direction and force of the wind, and also the angle at which the wind struck the chimney-pot. He considered the paper a good one, and a step in the right direction.
[1]. The prognostics quoted in the paper have been mostly taken from the following works:
“Popular Weather Prognostics of Scotland.” By Arthur Mitchell, M. D., Edinburgh, New Philosophical Journal. “Weather Lore.” By Richard Inwards, F. M. S., London, 1869. “A Handbook of Weather Lore.” By Rev. C. Swainson, M. A., Edinburgh, 1873.
[2]. The calculation on which his remark on halos was founded is as follows:
Rain occurred in connection with—
| Solar halos. | Lunar halos. | ||||||
|---|---|---|---|---|---|---|---|
| Direction of wind | S. | SW. | W. | S. | SW. | W. | |
| Number of observations | 22 | 28 | 59 | 8 | 11 | 21 | |
| Rain within forty-eight hours | per cent | 79 | 78 | 81 | 50 | 91 | 76 |
| Rain on third day | do | 9 | 3 | 7 | 40 | 9 | 0 |