Intelligence and Miscellaneous Articles. 325 



tioned, there are a great number of partial and local facts, arising 

 from unequal tension in the more or less variably distributed elec- 

 tricity, whether negative or positive, with which the terrestrial 

 globe and its atmosphere are respectively charged. Such are those 

 which M. Matteucci observed, and those to which I have alluded 

 in this note ; such, moreover, are the ordinary storms, and all the 

 varied phenomena which accompany them. The attraction of 

 clouds by mountains, and the phenomena of phosphorescence which 

 they sometimes present, arise from the same cause ; and it is probable 

 that many other natural phenomena, waterspouts for example, have 

 the same origin. — Comptes Rendus, June 10, 1867. 



ON BREWSTER S NEUTRAL POINT. BY PLINY EARLE CHASE. 



In the April Number of the Philosophical Magazine Sir David 

 Brewster says, " Dr. Rubenson has never been able to see, even 

 under the fine sky of Italy, the neutral point which I discovered 

 under the sun, and which, I believe, has never been seen by any 

 other observer than M. Babinet." 



The point in question can be easily seen in Philadelphia on any 

 clear day when the sun is more than 20° above the horizon, and I 

 have reason to believe that it can be found with equal ease at many 

 other places in the United States, although I have not been able to 

 find any published observations except my own. 



As all the phenomena of skylight polarization are very interesting, 

 and as some of its laws are still imperfectly understood, others may 

 perhaps be induced to turn their attention in this direction, so as to 

 determine whether the difficulty experienced by European observers 

 is owing to a higher latitude, to a moister atmosphere, or to some 

 other cause. 



A simple Savart polariscope is sufficient for making the observa- 

 tions. In positing Brewster's neutral point I have usually raised the 

 lower sash of an attic window so that the bottom of the sash would 

 screen the sun from the polariscope. I have thus been able, in every 

 instance when the atmospheric conditions seemed favourable, to see 

 very distinctly the neutral point, and the oppositely polarized bands 

 above and below. — Silliman's American Journal for July 1867. 



NOTE ON THE FORCE WHICH THE MUSCLE OF A FROG CAN DE- 

 VELOPE IN CONTRACTING. BY M. J. ROSENTHAL. 



The height to which a muscle can raise a weight depends, as is 

 well known, on the length of its fibres. On the contrary, the force 

 of contraction, which is measured by the weight necessary to prevent 

 contraction, only depends on the extent of the transverse section of 

 the muscle, or on the number of fibres which compose it. 



M. E. Weber of Leipzig measured this force, and found it equal to 

 about 600 grammes for the unit of transverse section — that is, for a 

 square centimetre of muscle. M. Schwann also has shown that this 

 force is not constant in all cases, but depends on the state of con- 

 traction of the muscle — that is, that this force, being greatest in the 



