March 7, 1890.] 



SCIENCE. 



161 



encounter, I may commence by giving: an account of the rain 

 theories which have been popularly adopted by meteorologists. 

 These have been condensed in the following words by Mr. 

 Scott:— 



' 'Rain is produced by the chilling of air more or less charged 

 with moisture. This is effected in various ways, of which the 

 following are the principal: No. 1. The ascent of a current of 

 damp air, which is chilled as it rises; No. 3. The contact of 

 warm and damp air with the colder surface of the ground, as in 

 case of our own west coasts in winter [England] , where the land 

 is colder than the sea-surface ; No. 3. The mixture of masses of 

 hot and cold air." 



In the first place, it seems strange that rain should be caused 

 by the chilling of the atmosphere, as rain is almost invariably 

 accompanied by milder weather. A certain type of mild weather 

 is nearly always the forerunner of rain. During the rain the 

 temperature hardly sinks, although the sun is prevented from 

 shining on the ground ; and we generally expect warmer weather 

 to follow after the rain. These remarks may serve to rouse sus- 

 picion against the theory of rain being caused by chilling, for 

 we may feel perfectly sure that any theory which goes straight 

 against the general weather indication must be wrong from the 

 outset. However, let us now examine the theory in detail. 



Of these three causes, No. 3 is by the author himself placed 

 hors de combat, when he states that Dr. Haun of Vienna has 

 calculated, ' 'that even by assuming a very extreme case, which 

 could hardly occur, in nature, there could not be produced as 

 much as the twentieth part of an inch of rain. ' ' 



Cause No. 3 is by the author partly included in cause No. 1, as 

 the sloping land-surface causes the air moving against it to as- 

 cend. As to the other part of it, I fail to see how contact be- 

 tween a cold surface and warm air can produce rain. It can pro- 

 duce deposit of dew, as, for instance, when we bring a glass of 

 cold water into a heated room ; but rain always falls from a con- 

 siderable distance from the ground, and is therefore not created 

 at the place of contact of the air with the land-surface. 



We are therefore now reduced to cause No. 1 as the only possi- 

 ble cause of rain. This is, however, worse than any cause at all, 

 as may be seen from the following simple and well-known ex- 

 periment. If, under the piston of a strong glass cylinder, we 

 have air saturated with moisture, and press the piston down, a 

 portion of the moisture is condensed into water, as is seen by the 

 mist formed, and the trickling of dew down the inner surface of 

 the glass vessel. The temperature is raised by the compression, 

 but not sufficientlyto prevent condensation from taking place. If 

 we now draw the piston back to its first position, we find the air 

 under the piston in the same condition as when we started the 

 experiment. But this means, that, by expanding the air, the 

 moisture which was condensed into water by the compression has 

 again evaporated. The air, therefore, gets chilled by the ex- 

 pansion, but not sufficiently to prevent this evaporation from 

 taking place. 



The consequence is, that the chilling produced by expansion 

 during the ascent of a current of damp air can under no circum- 

 stances cause condensation of its moisture into rain. The ex- 

 periment, however, shows that condensation or rain can be pro- 

 duced by a body of saturated air being brought under greater 

 pressure ; and of this we will just make a passing note. 



The modus or the ascent of a current of damp air is by most 

 meteorologists considered to be the chief cause of rain, and is sup- 

 posed to take place at the centre of a cyclone. It is thus main- 

 tained that there is a certain inward movement of the circulating 

 surface-air in a cyclone, and that for the air (this is supposed to 

 be always damp air) which is can-ied by it towards the centre 

 there is no other means of escape but to rise at the centre. How 

 absurd this whole explanation must appear to anybody who has 

 been living in deserts or arid districts, will be observed when I 

 mention, that, while I was in Australia during a period of very 

 severe drought, a break in the drought was caused by a series of 

 cyclones crossing the country,' entering in the northern part 

 of New South Wales, and passing out again through Victoria, 

 thereby drenching a narrow strip of land about 50 miles wide and 

 ' See H. C. Russel, Report on Baiiitall of New South Wales. 



400 or 500 miles long with rain, while on both sides the drought 

 continued uninterruptedly. It seems difficult to explain how 

 this cyclone should have gathered its supply of moisture from 

 moisture rising from the dry surface-air over a perfectly dried- 

 up country. 



What we want is evidently a rain theory which is capable of 

 accounting for rain, whether the surface over which a cyclone 

 passes is wet or dry, or whether it is giving off vapors or not ; 

 and I have taken pains to show how utterly incapable the ex- 

 isting theories are in this respect, so as to clear the atmosphere 

 from old cobwebs which might stand in the way of an entirely 

 different view of the whole question, being well aware of the 

 opposition with which new theories are generally met at the be- 

 ginning. 



In my pamphlet on drought I called attention to the aqueous 

 vapor as the element of the atmosphere to which some unknown 

 quality was likely to adhere, and by knowing which we should 

 be able to explain the whole atmospheric puzzle. With the ob- 

 ject in view of finding this secret, I undertook in April, 1888, a 

 series of observations from the tower of the Eouen Cathedral in 

 France. 



The object of these observations was to ascertain the difference 

 in barometrical pressure existing between the two ends of averti- 



cal air-column, and to observe how far and in what manner this 

 difference, or the weight of the air-column, changes when the 

 state of humidity of the air varies. At the base and top of the 

 steeple of the cathedral, which is upwards of 500 feet high, was 

 established a station containing quicksilver barometers (and ane- 

 roid barometers to check the readings of these) and dry and wet 

 bulb hygrometers. At convenient places between the two sta- 

 tions, thermometers were hung out with the object of attaining a 

 fair average of the temperature of the air-column. 



The two stations were connected with a telephone ; and at con- 

 venient hours, at any time during the day or night, for a period 

 of about fourteen days, synchronous readings of all instruments 

 were taken at both stations. 



The instruments were the best and newest made by Messrs. 

 Negretti and Zambra of London, and were all adjusted at the 

 Kew Observatory. It is my pleasant duty to mention here that 

 this well-known firm of instrument-makers wrote me a polite 

 letter, in which they offered the loan of their instruments free 

 of charge, considering the interest involved in my researches. 

 To assist me in making these observations, I secured the services- 

 of Mr. McClellan of the Greenwich Observatory, who has had 

 many years' experience in handling the most delicate meteorolo- 

 gical instruments. 



Thus every thing possible was done to obtain reliable observa- 

 tions, and the result was as stated below. Instead of reproducing 

 here the figures of my own personal observations, I think it will 

 be more to the purpose to point out how the same result can. be 



