DliCEMBEK 14, 1S83. 



SCIENCE. 



761 



storm : hence here, also, other causes than rain 

 determine tiic general easterly progression. 

 Wliatever effect rain would have is over- 

 come by stronger canscs. The separa- 

 tion of a cyclone into two independent 

 storms is jirobably aided by the irregu- 

 lar distribution of rain. 



Ine(inality in the strength of the inblow- ^- 

 ing winds is a result of irregular distri- 

 bution of barometric pressure in the re- 

 gions around the storm ; and the stronger 

 indraught will come from the higher press- 

 ure, because the grad-cnts will bo steep- 

 est on that side. Taus, in the case of 

 the West India hurricanes, the higher 

 pressure is to the north or north-east in 

 the ' horse latitudes ' above named, and tlie 

 lower pressure to the south, near the equator ; 

 and the northerly winds will therefore be 

 stronger than the southerlj'. The stronger 

 the wind, the greater its centrifugal force ; 



\ ^ ,,\ V ■ \ f :'k ' ^\ 



F[G. 16. 



and, if this is not equal on all sides, the centre 

 of lowest pressure will be drawn toward the 

 point where it is strongest. This will be where 

 it has to bend sharpl3' aroinid from its original 

 direction, and may average about 13.5^ from 

 the source of the wind : hence, if the stronger 

 wind come from the north-east, the storm- 

 centre will move west : if from the cast, north- 

 west, as in fig. 1 7 ; and soon. Consequently, 

 this cause will aid the first named in requiring 

 the storm to describe a curved track in passing 

 from the torrid to the temperate zone. It will 

 also aid the coalescing of two neighboring 

 storms, which has not unfrequently been ob- 

 served ; but, as a rule, it plays a subordinate 

 part in determining the direction of advance. 

 The slower advance of such of our storms as 

 have extra strong winds on their western side 

 (Loomis) is probably also due to this cause. 



The fourth cause of a storm's advance is a 

 peculiar effect of the deflective force arising 

 from tiic earth's rotation. It has already 

 been shown that this force increases toward the 



poles : it will therefore be greatest on" the 

 polar side of a cyclone ; and the greater the 



storm's diameter, the more marked the differ- 

 ence between the two sides. Its effect will be 

 to make the centrifugal force on the two sides 

 unequal, as in the previous cause ; but the 

 resultant motion will here be always from 

 the equator. In the absence of other causes of 

 motion, cyclones would therefore move along 

 meridians : as it is, thev nearly- alw.ays have 

 a more or less pronounced polar tendency , 

 and their failure to move directly from the 

 equator is due to the other causes of progres- 

 sion already mentioned. 



(To be continued.) 



A COMBINATION WALNUT. 



A PEcuLiAU nut has recently been sent lo 

 me from Mr. S. L. Bingaman, Pughtown, Ches- 

 ter county, Penn. It was found on his lawn 

 under a black-walnut tree (.Juglans nigra). 

 Mr. Bingaman says, "There is a pecan about 

 sixty feet from it [tiio walnut-tree], and a 

 shellbark some three hundred yards oft" 

 The nut is divided into two parts, as viewed 

 upon the outside. 

 There is a small por- 

 tion at the base end, 

 which has a covering 

 similar to that of a 

 black walnut. The 

 upper and larger part 

 of the nut has a cov- 

 ering closely resem- 

 bling that of a sliell- 

 l)ark (Carya alba). 

 Tiiis exocarp is four- 

 valved, and a [jartial 

 separation lias taken 

 place at the ui)|)erend. 



In its texture and adherence to the shell this 

 covering is much like that of the ordinary black 

 walnut. Upon cutting the nut in two. the shell 



