340 On "Refraction, 



I gave him the same quantity as before (viz. ol. tercb. 

 rect. et syr. croci aajj). This produced violent retchings, 

 tenesmus, strangury, and great pain in the back ; the urine 

 was also a little tinged with blood. The strangury and 

 tenesmus continued nearly a week, and the patient was not 

 able to work for several days after. As he had not voided 

 any portion of worm with the last dose, I concluded that 

 he was quite well, but requested he wou4d call on me again 

 in about two months. He called last week, and T advised 

 him to try his old remedy (a drachm of jalap), which had 

 its usual effect, in bringing away a large quantity of the 

 worm. I fear I shall not be able to induce him again to 

 try the ol. tereb., from the severe symptoms which U pro- 

 duced when he last used it. 



Aug. 27, 1810. 



LXIII. A short Account of the Improvements gradually 

 made in determining the Astronomic Refraction, By 

 T. S. Evans. 



X he principal object which the astronomer has in view, 

 is to determine the real places of the heavenly bodies, from 

 the apparent ones observed from a point situated on the 

 earth's surface. In general, it is necessary to reduce them 

 to what they would have been found, were the observer 

 situated in the sun's centre : and it is very seldom that they 

 do not require to be reduced to some other point. Various 

 equations and corrections are of course necessary for this 

 purpose, but none of greater importance than the refraction, 

 which is caused by the atmosphere that surrounds the earth, 

 and produces in' every ray of light that traverses it, a greater 

 or less deviation from its rectilinear course, according to 

 the density of the air, and the altitude of the object above 

 the horizon. Perhaps there is nothing that has opposed so 

 great an obstacle to the improvement of astronomy as re- 

 fraction, and nothing requires greater attention by every 

 one who makes observations of any accuracy, since there 

 are very strong reasons for presuming that it is different,' in 

 some degree, in almost every different situation. Most of 

 the principal astronomers from Tycho Brahe down to the 

 present time have done something which tended to improve 

 the method of finding it : but further observations and 

 experiments are still wanting, for there is, even now, an 

 uncertainty of several seconds in it, at low altitudes. To 

 bring under one point of view, aud in the compass of a small 



sketch, 



