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Sect. IX.] 



METEOROLOGY. 



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squalls, or other circumstances of interest ; the direction 

 of the wind as well as its force should be registered at 

 each observation; and for tliis it is well to hav- asmal) 

 compass with a vane of card, or thin and very moveable 

 sheet brass, which may be fastened on the top of the 

 anemometer, and which will indicate the direction in 

 which its opening should be turned. In concluding the 

 direction and the force of the wind from the vane and 

 anemometer readings, a correction depending on the 

 direction and velocity of tbe ship's motion is required in 

 strictness. But such corrections are not usuaUi/ applied, 

 and it may be doubted whether the observations can be 

 acciu-ately enough made to render it worth while to 



apply them. 



The Actinometer consists of a large hollow cylinder of 

 glass, soldered at one end to a thermometer-tube, termi- 

 nated at the upper end by a ball drawn out to a point, and 

 broken off, so as to leave the end open. The other end 

 of the cylinder is closed by a silver or silver-plated cap, 

 cemented on it, and furnished with a screw, also of silver, 

 passing through a collar of waxed leather, which is pressed 

 into forcible contact with its thread, by a tightenin 

 of large diameter enclosing it, and working into the silver 

 cap, and driven home by the aid of a strong steel key or 

 wrench, which accompanies the instrument. 



The axis of this screw is pierced to allow the stem of 

 a spirit thermometer to pass out through it, the bulb (a 



very long one) 



perature of the enclosed liquid. 



screw 



The graduation is in 



the stem of the screw, which is prolonged to receive ana 



defend it. 



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