614 OCULAR SPECTRA. Stcj. XL 9, 10. 



The locked jaw, and fotne cataleptic fpafms, are 

 refembled by this phenomenon ; and from hence 

 we may learn the danger to the eye by infpecling 

 very luminous objects too long a time. 



IX. A quantity of Jlimulus greater tlian the preceding 

 induces a temporary paralyfis of the organ ofvijion. 



1. PLACE a circular piece of bright red filk, 

 about half an inch in diameter, on the middle of a 

 fheet of white paper ; lay them on the fioor in a 

 bright funfhine, and fixing your eyes (teadily on the 

 center of the red circle, for three or four minutes, 

 at the diftance of four or fix feet from the object, 

 the red filk will gradually become paler, and finally 

 ceafe to appear red at all. 



2. Similar to thefe are many other animal facts ; 

 as purges, opiates, and even poifons, and contagi- 

 ous matter, ceafe to fUrriulate our fyftem, after we 

 have been habituated to their ufe. So fome people 

 fleep undifturbed by a clock, or even by a forge 

 hammer in their neighbourhood : and not only con- 

 tinued irritations, but violent exertions of any kind, 

 are fucceeded by temporary paralyfis. The arm 

 drops down after violent action, and continues for 

 a time ufelefs ; and it is probable, that thofe who 

 have perifhed fuddenly in fwimming, or in fcating 

 on the ice, have owed their deaths to the paralyfis, 

 or extreme fatigue, which fucceeds every violent and 

 continued exertion. 



X. MISCELLANEOUS REMARKS. 



THERE were fome circumftances occurred in 

 making thefe experiments, which were liable to alter 

 the refults of them, and which I fhall here mention 



for 



