S64 SCIENCE OF AGRICULTURE. Part II. 



longer this lightning continues, the less dense does the cloud become, and the less dark 



its appearance j till at length it breaks in different places, and shows a clear sky. Those 



thunder-clouds are said to be sometimes in a positive as well as a negative state of 



electricity. The electricity continues longer of the same kind, in proportion as the 



thunder cloud is simple and uniform in its direction ; hut when the lightning changes 



its place, there commonly happens a change in the electricity of the atmosphere over which 



the clouds passed. It changes suddenly after a very violent Hash of lightning; hut 



gradually when the lightning is moderate, and the progress of the thunder-cloud slow. 



£397 Lightning is nn electrical expiation or 'phenomenon. Flashes of lightning arc usually seen in 

 broad ami undefined masses; when their path appears angular or zigzag, they are reckoned most 

 dangerous, They strike the highest and most pointed objects in preference to others, as hills, trees, spires, 



masts id ships, ,\c. ; so all pointed conductors receive and throw oil' the electric fluid more readily than 

 those that an- term n Ited by flat surfaces. Lightning is observed to take and follow the readiest and best 

 Conductor ; and the same is the case with electricity in the discharge of the Leyden phial ; whence it is 

 inferred, th.it in a thunder-storm it would be safer to have one's clothe' wet than dry. Lightning burns, 

 dissolves metals, rends some bodies, sometimes strikes persons blind, destroys animal life, deprives magnets 

 of their virtue, or reverses their poles ; and all these are well known properties of electricity. 



With regard In plttiet of safety in times of thunder and lightning. Dr. Franklin's advice is to sit 

 in the middle of a room, provided it be not under a metal lustre suspended by a chain, sitting on one chair, 

 and laying the feet on another. It is still better, he says, to bring two or three mattresses or beds into the 

 middle of the room, and folding them double, to place the chairs upon them; for as they are not so good 

 Conductors as the walls, the lightning will hot be so likely to pass through them. But the safest place of all 

 is in a hammock hung by silken cords, at an equal distance from all the sides of the room. Dr. Priestley 

 ob s erv es, that the place Of most perfect safety must be the cellar, and especially the middle of it ; for when 

 a person is lower than the surface of the earth, the lightning must strike it before it can possibly reach him. 

 In the fields, the place of safety is within a few yards of a tree, but not quite near it. Beccaria cautions 

 persons not always to trust too much to the neighbourhood of a higher or better conductor than their own 

 body, Mine he has repeatedly found that the lightning by no means descends in one undivided track, but 

 that bodies of various kinds conduct their share of it at the same time, in proportion to their quantity and 

 conducting power. 



Sect. II. Of the ~\reans of Prognosticating the Weather. 



2399. The study of atmospherical changes lias, in all ages, been more or less attended to 

 by men engaged in the culture of vegetables, or the pasturage of animals ; and we, 

 in this country, are surprised at the degree of perfection to which the ancients attained in 

 this knowledge : but it ought to he recollected, that the study of the weather in 

 the countries occupied by the ancients, as Egypt, Greece, Italy, and the continent 

 of Europe, is a very different thing from its study in an island situated like ours. It is 

 easy to foretell weather in countries where months pass away without rain or clouds, and 

 where some weeks together, at stated periods, are as certainly seasons of rain or snow. It 

 may be asserted with truth, that there is a greater variety of weather in London in 

 one week, than in Rome, Moscow, or Petersburg!) in three months. It is not, there- 

 fore, entirely a proof of our degeneracy, or the influence of our artificial mode of living, 

 that we cannot predict the weather with such certainty as the ancients ; but a cir- 

 cumstance rather to be accounted for from the peculiarities of our situation. 



2400. A variable climate, such as ours, admits of being studied, both generally and lo- 

 cally ; but it is a study which requires habits of observation and reflection like all other 

 studies ; and to be brought to any useful degree of perfection must be attended to, not as 

 it commonly is, as a thing by chance, and which every body knows, or is fit for, but as a 

 serious undertaking. The weather may be foretold from natural data, artificial data, and 

 from precedent. 



2401. The 7iatttral data for this study are, I. The vegetable kingdom ; many plants 

 shutting or opening their flowers, contracting or expanding their parts, &c. on ap- 

 proaching changes in the humidity or temperature of the atmosphere : 2. The animal 

 kingdom ; most of those familiar to us exhibiting signs on approaching changes, of which 

 those by cattle and sheep are more especially remarkable ; and hence shepherds are gene- 

 rally, of all others, the most correct in their estimate of weather : 3. The mineral king- 

 dom ; stones, earths, metals, salts, and water of particular sorts, often showing indications 

 of approaching changes: 4. Appearances of the atmosphere, the moon, the general cha- 

 racter of seasons, &c. The characters of clouds, the prevalence of particular winds, and 

 other signs are very commonly attended, to. 



2402. The influence of the moon on the weather has, in all ages, been believed by the 

 generality of mankind : the same opinion was embraced by the ancient philosophers; and 

 several eminent philosophers of later times have thought the opinion not unworthy 

 of notice. Although the moon only acts (as far at least as we can ascertain) on the waters 

 of the ocean by producing tides, it is nevertheless highly probable, according to the ob- 

 servations of Lambert, Toaldo, and Cotte, that in consequence of the lunar influence, 

 great variations do take place in the atmosphere, and consequently in the weather. The 

 following principles will show the grounds and reasons for their embracing the received 

 notions on this interesting topic : — 



840& There arc ten situations in the moon's orbit when she must particularly exert her influence on the 

 atmosphere ; and when, consequently, change's of the weather most readily take place. These are, — 

 1st, The neir, and 2d, The Jull moon, when she exerts her influence in conjunction with, or in opposition 



to, the sun. 



