48 POPULAR LECTURES AND ADDRESSES. 



is taken out to dry the sand, or to change its 

 quantity." 



Lieutenant Raper's anticipation, published first 

 in 1840, that the Massey log would come into 

 extensive, if not general, use, has been amply 

 verified. It is now to be found, I believe, on 

 board of almost every British ship, not running 

 at too great a speed for its use. It is the instru- 

 ment chiefly trusted for finding distances run at sea, 

 failing sights of sun or of stars ; and the old log-ship 

 and glass, though capable of doing very good work 

 in careful hands, has fallen, or is falling, into 

 general disuse. The Massey log is kept con- 

 tinually in tow when the ship is out of sight of 

 land, except for a few minutes occasionally, when 

 it is taken on board and its dial read off. Its 

 reckoning of the distance run in different con- 

 ditions of the sea and wind, in clear weather is 

 checked by the ordinary astronomical observations. 

 Then judging from the results, the navigator cor- 

 rects its indications, if necessary, before using them 

 to estimate the distance run in cloudy weather. 

 All the different kinds of logs, which I have now 



