16 THE AIR 



which should be placed forward of the funnels and 

 galley chimneys and on the highest accessible part of 

 the ship, so as to keep it freely exposed to the wind, 

 but clear of spray except in the worst weather. The 

 middle of the forward end of the roof of the chart-room 

 is the ideal position. Better results would probably 

 be obtained by the use of Assmann's aspiration 

 psychrometer. This consists of a wet and dry bulb 

 thermometer placed side by side in metal tubes, over 

 which air is drawn by a quick-running fan, actuated 

 by clockwork. It can be used in full sunshine, and 

 the observer should stand on the windward side of the 

 upper deck, the instrument being kept in a case safely 

 stowed away between the times of reading. 



Maximum and minimum thermometers of the 

 ordinary type could not be used on board ship hitherto, 

 on account of the liability of the indices to be displaced 

 by the rolling ; but on the largest vessels of the present 

 day there seems no reason why they should not be 

 employed with perfect safety on most days, if they are 

 placed fore and aft in the thermometer screen. But 

 in any vessel a maximum and minimum thermometer 

 of Six's type can be used alongside of the wet and dry 

 bulb thermometers, and the results of such observations 

 would be the more useful because, as yet, they are very 

 rare. The best form would be one of the large-pattern 

 deep-sea thermometers, which for this purpose need 

 not be provided with an outer protective bulb. A 

 thermograph hung by a spring hook from the roof of a 

 well-exposed Stevenson screen would yield most 

 interesting results, but everything depends on the 

 exposure being free to the wind and protected from 

 the sun, rain, and spray, while the clock would require 

 to be carefully attended to and set daily to ship's time. 



It would probably be of little use to attempt to 



