202 Report of the Meteorological Committee. [Jan. 20, 



" Thus much may, however, be said: — 



" A great contrast of temperature over a limited area, or, so to 

 speak, a great thermometric gradient, being an indication of serious 

 atmospherical disturbance, is a precursor or concomitant of a 

 storm. This fact has been clearly pointed out by Dove; but 

 more recent evidence on the same head is to be found in the cir- 

 cumstance that for five days, January 26-30, 1870, the mean of 

 the temperatures at 8 a.m. at London and Valencia differed 16°, 

 being 28° and 44° respectively, a heavy southerly gale blowing all 

 the time over Ireland. A more recent instance, in which a re- 

 markable contrast of temperature immediately preceded a very 

 serious storm, was on the 13th of November, 1875, when the 

 reading at Scilly was 57°, and at Wick 21°. These figures give 

 the very large difference of 36°. The gale of Sunday, November 

 14th, with its accompanying high tide, will be fresh in the me- 

 mory of all. 



"Another mode of utilizing temperature in the forecasting of 

 storms is to be found in the long-established fact that an abnor- 

 mally high temperature, close stuffy weather, frequently precedes 

 a storm. This principle has not been reduced to numerical 

 measure as yet. 

 " IV. Vapour-Tension and Rainfall. — Very much weight is attached 

 by several meteorologists to the indications obtainable from these 

 elements, as Mohn and Loomis consider that their disturbance 

 and intensity determine the direction and velocity of motion of 

 cyclones, and that even the very existence of a cyclonic disturb- 

 ance depends on the presence of aqueous vapour in abundance. 



" For the area of our storm-warning system this indication is ne- 

 cessarily of minor value, inasmuch as our district is so intersected 

 by water that no portion of it will show such contrasts in regard 

 of vapour-tension as subsist in continental stations. 

 " V. Sea- Disturbance. — This is at times a most valuable help towards 

 gaining a knowledge of comiDg storms ; but it is very untrust- 

 worthy. The sea-disturbance, being caused by the wind, is pro- 

 pagated in the direction in which that wind is blowing, not in that 

 in which it is advancing. Thus a very heavy sea may roll in on 

 our coasts without any gale reaching them; and conversely heavy 

 gales, even westerly gales, like that of November 22, 1872, may 

 come on without any premonition in the way of a ground-swell. 



" The distance to which waves may be propagated is indicated by 

 what has already been mentioned as probable, that the ' rollers ' 

 of Ascension and St. Helena may be due to N.W. gales in the 

 North Atlantic. 

 " VI. Local Signs. — These are really among the most important indica- 

 tions of coming change; but practically they can scarcely be 



