206 LIGHT SCIENCE FOR LEISURE HOURS. 



ture of 39, but some 12 or 14 lower. This, however, 

 does not affect Herschel's argument. If he had taken 

 a column whose base had a temperature of 25 instead 

 of 39, he would have had to extend, also, the range of 

 the water-slope in latitude ; and, in fact, he would have 

 obtained a yet smaller declivity in this way than that 

 actually deduced by him. Maury does not seem to 

 have noticed the really weak point in Herschel's argu- 

 ment. I shall presently show where this seems to me 

 to lie. 



But if Maury fails in efficiently defending his own 

 views, he certainly is sufficiently effective in his attack 

 upon Sir John Herschel's. 



He asks, in the first place, the pertinent question 

 6 How can the north-easterly trade-winds, which blow 

 only 240 days out of 365, cause the equatorial current 

 to flow all through the year towards the north-west 

 without varying its velocity either to the force or to the 

 prevalence of the trade-winds ? ' ' That the winds do 

 make currents in the sea, no one,' he says, 6 will have 

 the hardihood to deny ; but currents that are born of 

 the winds are as unstable as the winds; uncertain 

 as to time, place, and direction, they are sporadic and 

 ephemeral.' 



He then points to a fact which ' militates strongly 

 against the vast current-begetting power that has been 

 given by theory to the gentle trade-winds. In both 

 oceans, the Sargasso seas lie partly within the trade- 

 wind region ; but in neither do these winds give rise 

 to any current. The weeds are partly out of water, and 



