33+ THE POPULAR SCIENCE MONTHLY. 



Result : AVhen placed in the path of the beam, the spectrum disap- 

 j^eared, with the exception of the blue and violet end. To the eye the 

 spectrum was thus reduced to a single broad band of blue-violet light. 

 To the ear, however, the spectrum revealed itself as two bands of 

 sound, with a broad space of silence between. The invisible rays 

 transmitted constituted a narrow band just outside the red. 



I think I have said enough to convince you of the value of this new 

 method of examination, but I do not wish you to understand that we 

 look upon our results as by any means complete. It is (3ften more 

 interesting to observe the first totterings of a child than to watch the 

 firm tread of a full-grown man, and I feel that our first footsteps in 

 this new field of science may have more of interest to you than the 

 fuller results of mature research. This must be my excuse for having 

 dwelt so long upon the details of incomplete experiments. 



I recognize the fact that the spectrophone must ever remain a mere 

 adjunct to the spectroscope, but I anticipate that it has a wide and in- 

 dependent field of usefulness in the investigation of absorption spectra 

 in the ultra-red. 



-- 



PHYSICAL EDrCATION". 



By FELIX L. OSWALD, M. D. 

 SLEEP. 



"Cliildren, stinted in their sleep, are never wide-awake.''' Pestalozzi. 



THE vital processes of man, like those of all his fellow-creatures, 

 are partly controlled by automatic tendencies. Some functions 

 of our internal economy are too important to be trusted to the caprices 

 of human volition ; breathing, eating, drinking, and even love, are 

 only semi-voluntary actions ; and during a period varying from one 

 fourth to two fifths of each solar day the conscious activity of the 

 senses undergoes a complete suspense : the cerebral workshoj) is closed 

 for repairs, and the abused or exhausted body commits its organism 

 into the healing hands of Nature. Under favorable conditions eight 

 hours of undisturbed sleep would almost suffice to counteract the 

 physiological mischief of the sixteen waking hours. During sleep 

 the organ of consciousness is at rest, and the energies of the system 

 seem to be concentrated on the function of nutrition and the renewal 

 of the vital energy in general ; sleep promotes digestion, repairs the 

 waste of the muscular tissue, favors the process of cutaneous excretion, 

 and renews the vioror of the mental faculties. 



The amount of sleep required by man is generally proportionate 

 to the waste of vital strength, whether by muscular exertion, mental 



