490 



connect it with the bank or other boundary of the space of 

 water, loops being attached to their extremities for this pur- 

 pose. Such canvass could be easily spread out or hauled in, 

 and would effectually prevent, while over the water, any eva- 

 poration taking place, no matter how dry the atmosphere, or 

 how intense the heat of the sun. Neither would this method 

 have the inconvenience that at first it is apparently liable to, 

 of heating the water in the tank, &c. ; for we know that water 

 cannot be easily heated from above, inasmuch as the water 

 warmed at the surface becomes specifically lighter, and thus, 

 being incapable of sinking, forms a superficial stratum, which 

 prevents the propagation of the heat downwards. It is evi- 

 dent that by this method a considerable quantity of the cover- 

 ing, sufficient, indeed, to form a non-evaporating surface over 

 large ponds, water-holes, &c., might be carried by a single 

 horse. When an exploring party, so provided, arrives at a 

 pond, water-hole, &c., they can readily cover it, either by 

 carrying ropes round the piece of water, or by means of one 

 or two men swimming across, holding the ropes attached to 

 the edge of the canvass ; thus may be preserved for months a 

 supply, which, if left exposed to the absorbing influence of 

 the atmosphere, would have vanished in the course of a few 

 weeks. 



" The following extract from the work of Lieutenant- 

 Colonel Sir T. L. Mitchell, Surveyor- General of New South 

 Wales, proves that the preservation of water will hereafter 

 form in Australia the most essential feature in agriculture; 

 and consequently every means adapted to facilitate this ob- 

 ject, will be of the greatest value in that extensive field for 

 British colonization and enterprsie : — ' With equal truth it 

 may be observed, that there is no region of the earth suscep- 

 tible of so much improvement, solely by the labour and 

 ingenuity of man. If there be no navigable rivers, there are 

 no unwholesome savannas ; if there are rocky ranges, they 

 afford at least the means of forming reservoirs of water ; and 



