336 



Part III. — Fifteenth Annual Report 



sheet-lead, sufficient to all but submerge the wood, were then securely- 

 tacked on to one side, and another card to the other side : and the whole 

 was again dipped in paraffin. The object was to render it impervious to 

 water while allowing the print to be read through the translucent layer. 

 So long as they were floating, the drift-slips, as a rule, answered well, as 

 was shown both by direct experiments and by many of the results. But 

 when they lay on the beach for any length of time, subjected to the 

 tossing action of the waves and frictiou and abrasion on stones and sand, 













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Fig. 1. — Showing the two forms of float adopted in the experiments. 



the paraffin was apt to be more or less worn off and the print partially 

 obliterated. At first, too, another difficulty was encountered. The 

 paraffin and paper proved attractive to minute animals on the shore — pro- 

 bably Crustacea, such as Talitrus, which abounds in most places — and they 

 were eaten off, leaving curious patterns ; mixture of creosote and carbolic 

 acid with the paraffin obviated this difficulty. As has been said, however, 

 the wooden slips did not give such good results as the bottles. 



These floats were meant to ascertain the movement of the surface 

 water. ' Latterly, it was deemed expedient to discover, if possible, whether 

 the bottom water and the intermediate layers moved in the same direction 

 as the surface. A number of wooden slips were accordingly weighted so 

 as to sink gently to the bottom, but none have been recovered ; pro- 

 bably owing to the influences above alluded to. Bottles, carefully 

 arranged to resist pressure, and tested first, were also loaded with the 



