II a in. 331 



10. — Ceruravinula, Puss moth. 



11. — Bombyx mori, Silkworm moth. 



12. — Euproctis chrysorrhcea, Brown tail. 



13. — Pieris brassicce, White butterfly. 



14. — Epinsphile janira, Meadow brown. 



15. — Thecla betulce, Brown-hair streak. 



16. — Jodis vernaria, Small emerald. 



17. — Egg of Honey bee, showing germinal vesicle. 



RAIN. 



BY RICHARD A. PROCTOR, B.A., F.R.A.S. 



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 

 of those we are familiar with in England — are not phenomena 

 which suggest an impression of pow er. Yet the forces actually 

 called into action before rain can fall, are among the most 

 gigantic experienced on our earth. Compared with them, 

 terrestrial gravitation is more feeble than is the puniest infant 

 compared with an array of giants. Let us look 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 

 1 00 square miles to a depth of one inch in twenty-four hours. 

 Now, what is the expenditure of power of which such a phe- 

 nomenon is the equivalent ? The dowufall is, so to speak, the 

 loosening of the spring, but how much force was expended in 

 winding up the spring ? 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 which the moisture is discharged in rain. 

 But let us take this evaporation only, and estimate its real 

 force-equivalent. It may be shown by a calculation founded 

 on M. Joule's experiments, that to evaporate a quantity of 

 water sufficient to cover an area of 100 miles to a depth of one 

 inch, would require as much 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 required to 

 raise a weight of upwards of one thousand millions of tons to 

 a height of one mile ! I will run briefly through the calcula- 

 tion by which this last result is deduced from the well-known 



