208 



HARDWICKE'S SCIENCE-GOSSIP. 



a lump of ice into a fierce fire and watching the slow 

 progress of its fusion and evaporation. This simple 

 experiment is quite sufficient to demonstrate " the 

 manifest absurdity " of asserting that a fair-sized 

 hailstone could be fused, volatilised and dissociated 

 during the small fraction of a second which would be 

 occupied in its passing through our atmosphere 

 "with planetary velocity." The heat generated on 

 its surface could not penetrate with thawing effect 

 to a depth of as much as T Jj of an inch. 



The tropical hailstones above described are directly 

 and fully accounted for by Schwedoffs theory, but 

 require an extravagant strain of possibilities to 

 reconcile them with the text-book theories. Sir W. 

 Thomson writes admirably, but speaks as rashly as an 

 Irish M.P. 



Fulgurites. — At various times mysterious glass- 

 like tubes have been found in the earth, penetrating 

 to considerable depths in sandy soils. The earliest 

 account of them is by David Hermann, who de- 

 scribes in his book on the curiosities of Massel (a 

 town in Silesia) some tubes 20 feet long that he 

 found on a hill near the town. Their origin re- 

 mained a mystery until 1790, when a man took refuge 

 under a tree at Aylesford during a storm and was 

 killed by the lightning which travelled along his body 

 and a stick he held in his hand, and then penetrated 

 the soil beneath, making a hole, in the lower part of 

 which the grains of sand were fused at their angles. 

 This was observed and described by Withering, who 

 attributed the appearances presented to fusion by the 

 electric discharge, or "the electric fluid," as it was 

 called in those days. Abundant descriptions have 

 followed ; some tubes having a length of more 

 than 30 feet have been disinterred, the substance 

 of their walls being hard enough to scratch glass. 

 Such tubes were found in Cumberland and in 

 Macclesfield ; the latter described by Darwin, which 

 after running in a nearly straight line about 23 feet, 

 divided into several branches similar to forked 

 lightning, or as Hermann says, like the branches of 

 a tree. 



These fulgurites are usually found in sandy de- 

 posits, and Darwin suggests this may not arise from 

 any preference of the lightning for such ground, but 

 from the fact that in such localities the tubes are 

 more easily discovered. Something further may, 

 I think, be added to this, viz. that dryness and 

 consequent bad conduction is necessary. 



If the lightning strikes humid soil, it will be 

 diffused in all directions by conduction. In order 

 that it shall continue as a disruptive discharge, it 

 must in the earth, as in the air, have no side 

 conduction outlets. If such tubes were formed in 

 ordinary agricultural soils containing much humus, 

 (which is a fairly good conductor) they would be 

 abundantly discovered in the course of agricultural 

 operations. 



The Philosophy of Pruning Vines, &c. — 

 H. Mueller has investigated that subject lately. He 

 finds that the proper time for pruning vines, &c. , is 

 while the fruit is ripening, and that the pruning 

 should be directed against the young shoots. The 

 reason for this is that the young shoots require a large 

 quantity of sugar for their development and for their 

 respiration. In the course of my pedestrian excur- 

 sions through France, and other vine-growing 

 countries, I have observed the merciless pruning just 

 at the most vigorous growing periods, and compared 

 it with the common practice of our gardeners of 

 pruning fruit trees before the leaves are formed ; 

 cutting away the leaf buds and leaving the blossom 

 buds. 



Looking at the subject theoretically, it appears 

 desirable to allow the leaves to perform their functions 

 towards the nutrition of the whole tree up to a 

 certain stage, while the fruit is forming, and then to 

 cut them away, as the vigneron does, when they rob 

 the ripening fruit of its sugar. There may, however, 

 be practical grounds for the difference of practice 

 which some of the readers of Science-Gossip are 

 able to explain. 



The Influence of Forest trees on Climate. 

 — In the current volume of " Ciel et Terre," page 149, 

 is an interesting article on this subject, in which it 

 states the particulars of observations at various 

 stations, within and outside of forests, the distances 

 outside varying from 250 to 400 metres. The general 

 results indicate that during the day, the air of a 

 forest is in all cases cooler, and during the night 

 warmer, than that of the open country. The difference 

 is greater in the day than at night, i.e. the refrigerating 

 action of the forest dominates ; the mean temperature 

 of day and night taken together is lower. The 

 difference is greater in pine woods than in beech 

 woods. This is attributed to the greater protection 

 afforded by the former during winter in resisting 

 radiation from the soil. The mean difference in the 

 temperature of the air shows a variation from 0*9° to 

 1*3° Centigrade during the day, and from o* 6° to 0-9° 

 at night. The difference of temperature of the soil 

 at a depth of two feet was 3 ■ 4 Cent, cooler in summer 

 and O" 3 warmer in winter. These are mean differ- 

 ences. The difference is of course much greater at 

 the extremes of day and night temperature ; the forest 

 is much cooler at the hottest hours of the hottest days, 

 and much warmer at the coldest hours of the coldest 

 nights. 



Mr. B. G. Jenkins, F.R.A.S., has published an 

 admirable London Weather-chart for 1S87, based 

 upon his paper entitled " Forecasting the Weather." 

 It is a forecast of the movements of the barometer 

 and thermometer in London from June to December 

 of the present year. 



