EXAMINATION OF THERMOMETERS. 367 



(iuced singular disorders in certain sensorial impressions. The arm 

 which was made cataleptic did not perceive the difference between a 

 warm and a cold temperature. The eye on the affected side suffered 

 a cramp of the accommodative muscle, and lost at the same time its 

 normal sensitiveness to colors. The hypnotic condition can be ex- 

 plained only by hypothesis. All that is certain about it is, that it is 

 due to a raoditication of the nervous centers of the brain and spinal 

 marrow. 



The apparently voluntary motions of persons in this condition are 

 independent of their will, the sensorial impressions acting directly on 

 their motive apparatus. 



* 



EXAMINATION OF TIIEEMOMETEES AT THE YALE 



OBSERVATORY. 



Br Dr. LEONARD WALDO. 



ONE of the most useful institutions to science in England is the 

 Kew Observatory of the Royal Society, whose principal work for 

 the last quarter of a century has been to furnish accurate comparisons 

 of thermometers sent there by physicists, meteorologists, physicians, 

 and instrument-makers. The recognized benefits accruing to the sci- 

 entific world from this well-known and widely popular service at Kew 

 have caused the managing board of the Winchester Observatory of 

 Yale College to organize a service having the same ends in view under 

 the direction of the observatory. Although this work is but fairly 

 commenced, yet it has met with most gratifying success, and there 

 have been so many inquiries as to the methods and scope of this ser- 

 vice that the writer has ventured upon a description suitable for the 

 pages of the " Monthly," with the hope that in this form it may the 

 more readily come to the notice of the meteorologists and physicians 

 who are the most likely to be benefited by it. 



Few are aware of the errors found to exist even in the thermometers 

 of reputable makers. The well-known change which takes place with 

 age in every thermometer not infrequently amounts to a degree and a 

 half Fahrenheit within two years from the time the thermometer is 

 made. The change depending upon the temperature to Avhich a ther- 

 mometer is heated, even supposing this to be no greater than the 

 boiling-point of water, may be three fourths of a degree. If we add 

 to these two sources of error the original error in the graduation of the 

 thermometer scale arising from the boiling and freezing points not 

 being properly fixed, and the error arising from the variations in the 

 size of the capillary tube, it is quite within the range of possibility 

 that thermometers, which from their general construction would appear 



