10 President's Address 



that it was not exactly of a nature included within 

 the objects of the Society : very little consideration must 

 however show, that any attempt to contribute to social 

 improvement, so long as it is regarded in its scientific 

 aspect, may be fairly considered to come within the scope 

 of this Society. 



6< The Danger of Collision between Vessels crossing one 

 another's Tracks," was the title of a communication from 

 Captain Perry, read to you at the November meeting. In 

 this paper a very simple method of procedure to be adopted 

 by approaching vessels was suggested by the writer, by 

 which danger of collision might in nearly all cases be 

 avoided. The plan suggested consists in the approaching 

 ships ascertaining if the same relative bearings between 

 them continues to be maintained, and if so, to alter 

 their course ; for, as was demonstrated by a simple diagram, 

 collision becomes inevitable if the same bearing is main- 

 tained. So simple a mode of even lessening the probability 

 of collisions, if not already generally adopted by nautical 

 men, should be well noted. 



At the same meeting a paper " On the Purification of 

 Water," was presented by Mr. Dahlke. This related to a 

 method of filtration devised hy the writer, by which organic 

 and most mineral impurities, including the salts of lead, 

 were removed from chinking water ; brackishness also, by a 

 judicious arrangement of this filtering medium, he stated 

 might be removed to a considerable extent. He exhibited a 

 filter that he had constructed which was partly tested in 

 your presence ; the further testing of its properties you will 

 remember was referred to Mr. Newbery, who reported at 

 the next meeting that the filter not only did all that Mr. 

 Dalhke had stated, but he found it to possess powers of filtra- 

 tion beyond anything he had previously known ; he had 

 tried it very severely by filtering solutions of salt, sulphate 



