40-1 Royal Institution : — 



teristics, those expected to be principally prevalent (with but few 

 exceptions) the following- day and the next after it, including the 

 nights — not those of the weather actually present — are cautiously 

 expressed after careful consideration. 



It may now be seen, after many months' trial, whether tolerably 

 correct forecasts of ordinary weather can be formed here sooner than 

 at distant isolated places, where the published general Reports arrive 

 a day or two later, and whether they are practically useful as con- 

 clusions available for the public. 



Ordinary variations of cloudiness, or clear sky, or rain, of a local 

 or only temporary character, are not noticed usually. 



That a broad general average or prevalence is kept in view, referring 

 to a day or more in advance, and to a district rather than only to 

 one time or place, should be remembered. 



The great practical difficulty is in separating the effect, on the 

 mind, of present states of air, weather, and clouds, from abstract 

 considerations of what may be expected on the morrow, or next fol- 

 lowing day. 



When in doubt, distrusting the indications or inferences from them 

 (duly considered on purely scientific principles, and checked by 

 experience), the words "Uncertai?i" or "Doubtful" may be used 

 without hesitation. 



As meteorological instruments usually foretell important changes 

 by at least a day, or much longer, we have to consider what wind 

 and weather may be expected from the morning observations com- 

 pared with those of the days immediately previous, as indicative of 

 the morrow's weather, and of the day after, at each place — to take an 

 average of those expectations for each district collectively in groups, 

 and then to estimate dynamical effects. 



Outline maps with moveable windmarkers, and cyclone-glasses or 

 horns, are useful in forecasting weather ; and full consideration 

 should be given to the probable position, direction, extent, and 

 degree of progress of that centrical area or node round which the 

 principal currents usually circulate or turn as they meet and alter, 

 combine with, or succeed one another. 



Here dynamical considerations, with comprehensive comparisons 

 of statical facts, are most important ; and to treat them even approxi- 

 mately well, with such quick despatch as is requisite, demands apti- 

 tude and experience. 



Those who are most concerned about approaching changes, who 

 are going to sea, or on a journey, or a mere excursion, — those who 

 have gardening, agricultural, or other out-door jDursuits in view, may 

 often derive useful cautionary notices from these published expecta- 

 tions of weather, although (from the nature of such subjects) they 

 can be but scanty and imperfect under present circumstances. 



Objection has been taken to such forecasts, because they cannot 

 be always exactly correct for all places in one district. It is, however, 

 considered by most persons that general comprehensive expressions 

 in aid of local observers, who can form independent judgments from 

 the Tables and their own instruments respecting their immediate vici- 



