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Page:Popular Science Monthly Volume 18.djvu/381

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EXAMINATION OF THERMOMETERS.

duced 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 explained only by hypothesis. All that is certain about it is, that it is due to a modification 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 THERMOMETERS AT THE YALE OBSERVATORY.
By 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 scientific 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 service 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 which a thermometer 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