124 



SCIENCE. 



{[Vol. XVIII. No. 447 



convolution of opposite phase, and all the while progressing in a 

 general direction parallel to the axis of motion. At this point it 

 may be asked, what advantage is secured by this curvilinear mo- 

 tion ? The chief advantage seems to be that those portions of the 

 body placed transversely to the axis of motion furnish better fulcra 

 from vehich the anterior parts of the body may be projected for- 

 ward. If this is the correct explanation, then, during the forward 

 movement of that part of the body anterior to the transverse 

 flexure, the scutes are for the most part passive, and the anterior 

 parts are projected by the median muscles. This seems to be a 

 good reason for believing that the scutes do not act in continuous 

 succession from before backwards, but intermittently and perhaps 

 to some extent simultaneously, being interrupted by shoves and 

 pulls which annul and complicate their action. The problem of 

 their motion, however, is a difiScult one, and more experimentation 

 is needed before the laws pf their action can be confidently and 

 fully formulated. J. Lawton Williams. 



HornellsvlUe, N.T., Aug. 18. 



Black and Bright Bulb Thermometers in Vacuo. 



In reply to an inquiry in this journal for Aug. 7, I would say 

 that the formulse for these radiation thermometers will be found 

 in the "Annual Report of the Chief Signal OfScer for 1885," pp. 

 131-134. Professor Ferrel has also made an exhaustive study of 



a special investigation of a large number of these thermometers, 

 which will be found in " Professional Papers, Signal Service,"" 

 XIII., pp. 34-50. 



Several notices have appeared in Nature from time to time. It 

 would seem that serious discrepancies have been found in these- 

 instruments, and it is still a mooted question as to their source. 

 Professor Ferrel found, as was to be expected, that the ventilation, 

 of the bulbs was a most important factor. H. A, Hazen. 



Washington, D.C., Aug. 18. 



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