TRANSACTIONS OF SECTION G. 501 



The determination of the percolative capacity at saturation point has a practical 

 bearing, as it is probable that the soil is capable of passing twice as much per 

 minute as the average percolation from rainfall in a day. Also, because irrigation 

 sewage works exist on gravel and other soils in which there are wells. The perco- 

 lative capacity under pressure bears on the yield of wells sunk in sands, &c, near 

 to and remote from large bodies of water upon the surface. 



Temperature of Percolatio7i. — The temperature of percolation has not been 

 observed. Changes of temperature in the soil must act upon the contained mois- 

 ture in the same way as they do in the air above, thereby tending to cause evapora- 

 tion or to produce percolation. In an abstract of more than 100,000 observations 

 upon the temperature of the soil made in the Gardens of the Royal Botanic 

 Society, London, 1871-1876, Mr. G. J. Seymour, F.R.S., shows that the heat wave 

 commences in March, and spreads downward till the whole 4 feet of observation 

 is warmer than the air in September and October ; the effect of the preceding cold 

 was disappearing at 4 feet by the end of August. In November the cold wave 

 commences and moves down till the whole 4 feet is colder than the air by the end 

 of February, when the heat wave begins again. This corresponds with the 

 division of Ebermayer on March 1 as regards the commencement of the heat wave 

 at the surface and the disappearance of the preceding heat wave at 4 feet ; and on 

 September 1 as regards the disappearance of the preceding cold wave at 4 feet, 

 but not as regards the surface, the heat wave lasting till the end of October. These 

 heat divisions correspond with the ' least rain ' periods of Glaisher which occur in 

 February and March, the last two months of the cold wave, and with the 'heaviest 

 rain ' periods which end with the heat wave at 3 inches in October ; with the 

 cessation of percolation in March (when the heat wave begins) and its recommence- 

 ment in November (when the cold wave begins). 



In reference to future observations on percolation, therefore, it is suggested 

 that :— 



1. Artificial admixtures should be avoided. 



2. The calibre of the constituent grains, and the percentage of grains of each 

 gauge in the natural admixture, should be experimentally ascertained. 



3. The absolute capacity should be measured. 



4. The retentive power should be proved. 



5. The percolative capacity at saturation point, and as far as possible at less 

 degrees of humidity, should be measured. 



6. The percolative capacities under pressure greater than that of saturation 

 should be proved. 



7. Percolators should contain thermometers. 



There should be a set of three cylinders — A, the saturated cylinder, filled with 

 saturated soil, closed top and bottom, and provided with a thermometer. 



B a common Dalton gauge, provided with thermometer. 



C the dry cylinder, filled with dry soil, closed top and bottom, and provided with 

 a thermometer. 



The thermometers should be arranged back to back in the centre of each percolator 

 at depths of 1, 2, 3, and 4 feet, and one at 3 inches and at the surface close to 

 them. Presumably the thermometers in the Dalton gauge would agree with those 

 in the dry gauge when the soil was dry, and with those in the saturated gauge 

 when the soil was saturated, as their difference would be noted. We should then 

 have something more than wet-and-dry bulb thermometers in the soil and the 

 machinery for connecting observations on rainfall, temperature, and percolation, and 

 ibr comparing different series of observations at present wanting. 



o. On Leon Francq's Fireless Locomotive. 

 By Mons. Charles Bergeron, C.E. 



Thejireless locomotive, described by Mons. Charles Bergeron, is an American 

 invention. It has been much improved by Mons. Leon Francq, civil engineer in 

 Paris, who studied the question of mechanical traction by means of steam engines 



