ALLISON ON TPIE METEOROLOGY OP HALIFAX. 183 



to the earth, and confines and throws back again Its lost tempera- 

 ture. Brechan tells us that Glaisher has observed passing clouds to 

 raise the temperature of raw wool, much cooled bv radiation, 15^ 

 in 15 minutes. Wind also, by transferring and mixing strata, 

 obstructs terrestrial radiation, and dew or hoar frost deposits. We 

 see now why a clear calm night is most favorable to these occur- 

 rences. Considering the above causes, it needs little reflection to 

 see that neither dew nor hoar frost is a sign of either fair or foul 

 weather to come. 



Let us take last year — 1871 — and observe what did actually 

 succeed these phenomena in the 131 instances recorded. I saw 

 hoar frost 43 times, and dew on 88 nights, with these results : — 

 On 19 occasions the days following deposits of hoar frost on the 

 previous evenings were without precipitation, giving 44 per cent, 

 against the prediction, and 56 in its favour, — while after 36 observ- 

 ations of dew appreciable rain fell, giving 41 per cent, adverse 

 to the popular creed, and 59 per cent in its favour. So that 

 regarding both forms of this phenomenon no certain conclusion, as 

 to their effect, can be arrived at, beyond the established fact that 

 their influence, if any, is not perceptible in the precipitation of the 

 24 hours immediately succeeding. In former papers — to be found 

 in the Transactions of this Institute for 1870 and '71 — I have 

 endeavoured to dispel the notorious idea that displays of aurora 

 are always followed by gales and foul weather ; and that a high 

 barometer must mean fine weather, and a low standing column the 

 opposite. These conclusions have been hastily formed in the 

 public mind from insufficient data ; and the instances when the 

 opinion has proved correct have left indelible marks upon the 

 judgements of superficial observers, while the contrary results have 

 readily faded from the willing memories. 



The truth is that the branch of the science including prediction, 

 is as yet scarcely shooting forth. No man, unaided by telegraphic 

 reports, can from his own observations at a single station, at present 

 prophecy the coming weather, beyond 24 or 36 hours, with any 

 approach to certainty. For this purpose, we now need — and 

 probably always shall need^ — reports at least twice a day from con- 

 nected stations. Having these, and the climatic peculiarities of our 

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