LIQUIDS AND ALUED EXPERIMENTS. 9 



m' being shown in the lapse of time. The curve is at first nearly linear in its 

 descent and thereafter is sharply flexed to the right. This is in a measure 

 due to the fact that much hydrogen has escaped, and the lower surface of the 

 bubble V is now no longer equal to the area or cross-section of the swimmer. 

 Hence the transpiration proceeds with diminished area, and therefore more 

 slowly. Subsequent experiments, however, will show that this flexure of 

 the curve is, in the main, real (§23). 



There are other difficulties which ultimately enter, owing to the fact that 

 the exhaustion needed to make the diver float is so large that the gases 



Table 2. — Molecular transpiration of hydrogen into air, through a wall of water. 

 i4 =0.005823; il/= 18.09 grams; pm=i3.6; i/p;, = 0.3486*; h' = o.o6 cm.; h"=\\.o 

 cm.; A'" = 5.5 cm.; 1 = 22.0 cm.; areas 12.6 cm. ^ and 24.6 cm.^; a = 12.0 cm.^; mean t, 

 22°; 7? = 4i.45Xio«; p/, = 89.55X lo-^. 



Date. 



191 1. Feb. 8 

 9 

 9 

 10 

 II 

 12 

 •3 

 •4 

 •5 



Hour, 

 afternoon. 



o 

 I 



4 

 4 

 o 



5 

 4 

 3 

 5 



m. 

 o 



30 



o 



o 



o 

 20 



o 



30 



o 



-mX 10' 



gms. /sec] 

 6.23 

 6.27 

 6.37 

 Mean: 

 6.29 



*Provisional value. See § 24. 



fTaken from four-day groups: Feb. 9 to 13; 10 to 14; 11 to 15. 



dissolved in the water come out, on exhaustion, prior to observation. 

 Hence all these results are discarded. To obtain a long period of trust- 

 worthy values the diver should either be weighted (a heavier diver will 

 hereafter be used) requiring more gas to float it, or the gas should be in 

 excess, so that the diver sinks only under excess of pressure. Both modi- 

 fications are in a measure undesirable. Massive parts endanger the accu- 

 racy of the temperature datum, and pressure excess requires a U-tube man- 

 ometer, which is less easily read at an instant than the barometric form. 

 Hence 



^^=1.07X10-'' ^^ = ^pi?T =1.31X10-' (§12) 



= 1.15X10-^^ 



(§13) 



Observations of the above kind, though exceptionally delicate in them- 

 selves, are marred by a difficulty which I have not quite been able to over- 

 come. Whenever the temperature differs from that of the room there will 

 be vortical convection currents, which by their friction on the walls of the 

 diver tend either to raise or to depress it. Hence such experiments should 

 preferably be made in a room of constant temperature (if available), or at 

 least in the summer. 



