TRANSMISSION OP SOUND-SIGNALS DURING FOGS AT SEA. 173 



not think this was the case in reality, for the difference in the results obtained 

 with distilled water and water containing 1 per cent, of salt is due to the 

 fact that in evaporating the solution of phosphate of lime a considerable 

 quantity of common salt is left, the removal of which necessitates the use of 

 distilled water. The washings necessarily contain a little phosphate of lime ; 

 hence the apparent diminished solubility of phosphate of lime in solutions 

 containing 1 per cent, of salt. 



Solubility of phosphate of lime in solutions containing 1 per cent, of nitrate of 



soda. 

 The following results were obtained in precisely the same way as in the 

 experiments with chloride of sodium : — 



Amount of phosphate 



1 



Exp. ■ 



Precipitated phosphate of lime in moist) 1st 

 condition J 2nd 



Commercial bone-ash J ~^ , 



2nd 



J 1st 

 I 2nd 



Suffolk coprolites , 



Cambridgeshire coprolites i ^^ , 



It appears from these experiments that nitrate of soda has no influence on 

 the solubility of phosphate of lime ; for the differences in the amount of phos- 

 phate of lime obtained from solutions containing 1 per cent, of nitrate of 

 soda, and from distilled water left in contact with phosphate of lime, are too 

 small to be due to any other cause than to the necessary errors which attach 

 to all analytical determinations of this kind. 



Provisional Report on the Present State of our Knowledge respecting 

 the Transmission of Sound-signals during Fogs at Sea. By Henry 

 Hennessy, F.R.S.^ Professor of Natural Philosophy in the Catholic 

 University of Ireland. 



In accordance with a request from the President and Committee of Section 

 A, I have drawn up the following provisional report on the state of our 

 knowledge relative to sound-signals during fogs at sea. 



It is unnecessary to enter into any details as to the methods in actual use 

 for signalling vessels during fogs. These methods are admittedly imperfect ; 

 they have been devised with little regard to scientific principles, and they do 

 not fulfil the purposes for which they are intended*. The objects to be at- 

 tained by sound-signals during fogs are twofold : first, to reveal the presence 

 of ships to each other, or of light-houses and beacons to ships ; secondly, to 



* Admiral FitzRoy furnishes an illustration, by an extract from a letter of the late Captain 

 Boyd, relative to a dense fog which prevailed in a part of the Irish Channel on the day be- 

 fore the ' Royal Charter ' storm. Only a few explosions from guns fired with full charges 

 fifom the seaward side of the flagship at Kingstown were heard on board the Holyhead 

 packet, when the distance of the latter did not exceed one mile. The fog-bell was heaid 

 when the packet was about half a mile distant, but only when the fog had lifted. We may 

 conclude, therefore, that as long as this fog rested on the water the bell was useless, and 

 the heavy firing was only partially useful. See " Storms of the British Isles. Tenth num- 

 ber of Meteorological Tapers, published by authority of the Board of Trade," p. 44. 



