2U 



♦ ?CN OWL EDGE ♦ 



[March 13, 1885. 



London and Xoitb- Western Railway from Leicester to 

 Nuneaton), fire miles from Leicester, we wa'k north- 

 wards for a nii'e to the syenite quarries at Enderby. In 

 the Lower Enderby quarry the igneous rock is seen 

 breaking through a greenish slate, i)robably of Cambrian 

 age; while abore the syenife a very tine section of Keiiper 

 sandstone and marl is se-n, the Triassic strata filling up 

 and resting in a long hollow in the syenite. In the 

 quarries at the top of the village — which is truly "founded 

 upon a rook " — it is interesting to note the manner in 

 which the syenite his weathered into immense balls. Re- 

 tracing our steps to Narborough, we examine a large 

 quarry there (the igneous rock heie is not shown on the 

 Survey Map), and then continue our walk for two miles in 

 a southwest direction, to Croft Hill, a coi.ical emii.ence 

 which lisps about 250 feet above the plain to a height above 

 sea-level of about 500 feet. The"Huncote" quarry here 

 is at the northern foot of the hill, and there is another 

 large quarry near Croft Station, which lies at the southern 

 extremity. Two miles to the west a similar rock forms the 

 low eminence — crowned by a mill — of Barrow Hill. Less 

 than two miles south of C'rofc we find the last exposure, in 

 a southerly direction, of the syenite round the villages of 

 Stoney Stanton and Sjpcote. 



At all the points named tie stone is largely quarried for 

 "setts" and "kerbs," many thousands of tons being sent 

 annually to London and other large towns, fetching a price 

 of from twenty to thirty shillings per ton. The stone is 

 extremely hard and tough, rather fine-grained, varying in 

 colour from gi-ey to pink, and composed of the mineials 

 felspar (pink) and hornblende (dull green), with a few 

 grains of quartz. Generally speaking there is little real 

 difierence between the rock and the syenites of Charnwood 

 Forest, and they may be all of the same geological age, 

 although what that age is— except that it is certainly pre- 

 carboniferous— is a very doubtful question. The ro"ck at 

 Barrow Hill shows an approach to the intrusive diorites 

 which traverse the Hnrtshill range— a few miles further 

 south. It is described by Professor Bonney as "a quartz 

 Jiorite rather than a syenite." 



RATX. 



By Richard A. Pkoctor. 



THERE are, perhaps, few natural phenomena which 

 appear less indicative, at first sight, of the operation of 

 nature's giant forces than the downfall of rain. Even 

 the heaviest showers — at least (f those we are familiar 

 with in England — are not phenomena which suggest an 

 impression of power. Yet the forces actually called 

 into action before rain can fall, are among the moat 

 gigantic experienced on our earth. Compared with them, 

 terrestrial gravitation is more feeble than is the puniest 

 infant compared with an army of giants. Let us lojk into 

 the matter a little closely, and we shall see that this is so. 



It is a common occurrence for rain to fall over an area of 

 100 square miles to a depth of one inch in twenty-four 

 hours. Now, what is the expenditure of power of which 

 such a phenomenon is the equivalent 1 The downfall is, so 

 to speak, the loosening of the spring, but how much force 

 was expended in winding up the spring 1 The evaporation 

 from the sea or from moist soils of the quantity of water 

 precipitated, is not the whole of the work to be estimated, 

 since_ the vapour has to be raised to the higher regions of 

 the air, and to be wafted by the winds— themselves the 

 representatives of giant forces— to the district over whith 

 t(je moisture is discharged in rain. But let us take this 

 evsporat:o.i cnly, and estimate its real force-equivalent. It 



may be shown by a calculation founded on Mr. Joule's 

 exptriments, that to evaporate a quantity of water suffi- 

 cient to cover an area of 100 miles to the depth of one inch, 

 would require as muth heat as is produced by the com- 

 bustion of half a million tons of coals ; and further, that 

 the amount of force of which such a consumption of heat 

 is the equivalent, corresponds to that which would be re- 

 quired to raise a weight of upwards of one thousand millions 

 of tons to a height of one mile ! I will run briefly through 

 the calculation by which this l-.st resirlt is deduced from 

 the well-known result of Joule's experiments that to raise 

 one pound of water one degree Fahrenheit, requires a 

 quantity of heat sufficient to rai.-e one pound to a height of 

 772 feet ; and the further experimental fact, that to raise a 

 pound of water from the liquid to the vaporous state, 

 requires 907 times as much heat as is required to raise the 

 same pound one degree Fahrenheit in heat. 



The amount of water required to cover one hundred 

 square miles to a dejith of one inch is, in volume — 



1,760 X 1,760 X 3 X 3 X 100 ^ 12 

 cubic feet, and as one cubic foot of water weighs 1,000 cz., 

 or nearly 03 pounds, we have in weight — 



1,700 X 1,760 X 3 X 3 X 8| X 62h pounds, 

 and to raise this weight of water 1° F., would require as 

 much heat as would suffice to raise to a height of on« rnile 

 a weight of — 



1,760 X 3 X Si X 62i X 772 pounds ; 

 while to vaporise the same weight of water would require 

 967 times as much heit. Thus we obtain a force sufficient 

 to raise a weight of — 



1,760 X 3 X 17 X 135 X 193 x 967 pounds, 

 (that is, nearly 1,020,000,000 tons), to the height of one 

 mile. 



Such is the amount of force, wh se effects are exhibited 

 in a day's steady downpour over a region of 100 i-quare 

 miles — for instance, over about one-tbird of ^Middlesex. 



The same amount of water falling iu the form of snow, 

 would repr-esent a yet greater expeuditure of force. "I 

 have seen," siys Tyndall " the wild stone-avalanches of the 

 Alps, which smoke and thunder down the declivities, with 

 a vehemence almost sufficient to stun the observer. I have 

 also seen tnowfiakes descending so softly as not to hurt the 

 fragile spangles of which they were composed ; yet to pro- 

 duce, from aqueous vapour, a quantity which a child could 

 carry, of that tender material, demands an exertion of 

 energy competent to gather up the shattered blocks of the 

 largest stone-avalanche I have ever seen, and pitch them to 

 twice the height fr-om whioi they fell. ' 



But it is when we come to estimate the fall of rain as a 

 terrestrial phenomenon — as a process continually going on 

 over large regions of the earth's surface, as a process in 

 which energies exhibited over one region are expended, 

 frequently, over regions thousands of miles away — that we 

 see the full significance of the drop of rain. We can well 

 understand how it is that "the clouds drop fatness on the 

 earth," when we estimate the powers expended in their 

 genesis. All the coal vs'hich could be raided by man from 

 the earth in thousands of years, would not give out heat 

 enough to produce by evaporation the earth's rain-supply 

 for one single year ! The sun — whose influence is often 

 contrasted with that of the rain-shower — is the agent in 

 producing that shower as well as in pouring out his direct 

 heat on the soil with such apparently contrasted elTect. 



The actual process of the production of rain has not yet 

 been completly explained. We are, in fact, doubtful as to 

 the true nature of clouds, fogs, and mist, and, therefore, it 

 is intelligible that some difficulty shou'd surround the 

 explanation of a phenomenon of which these meteors are, 

 so to speak, t!:e parents. 



