212 



Dr. J. T. Cash. 



Comparing this liability of error in the bisection of each star, in 

 obtaining its distance from tj, with the whole liability to error in dis- 

 tance, which is 0*24", it follows that probably the whole error in the 

 distance measures arises from the bisection, and that therefore the 

 film has remained undisturbed in the direction of distance. Another 

 practically important conclusion is that the exposure of the plates 

 should not continue beyond the time necessary to form distinct disks 

 of the stars to be measured, inasmuch as an increased enlargement 

 of the photographic image necessarily entails an increased error in 

 its bisection (see Table Y). Hence, if the stars to be measured differ 

 very greatly in magnitude, then it may be desirable to connect the 

 brightest stars with the fainter by means of stars of intermediate 

 magnitude. 



Such, then, appears to be the comparatively rigorous character of 

 photographic measurement : but I hope to carry the investigation still 

 further, by the application thereof to the determination of stellar 

 parallax, for which the method appears to be eminently adapted. 



Another investigation presents itself in the inquiry as to the effect 

 of atmospheric absorption at varying altitudes on the image im- 

 pressed. 



With regard to the question of the permanence of the film, it 

 would at present be premature to speak : it might be unsafe to 

 argue from the known permanence of the collodion plates on which 

 the lunar images are impressed, but so far as the present knowledge 

 suggests there is no evidence of deterioration. I propose, however r 

 to measure a few distances periodically, as well as the diameters of 

 the larger star disks. 



" Contribution to the Study of Intestinal Rest and Movement."" 

 By J. Theodore Cash, M.D. Communicated by T. Lauder 

 Brunton, M.D., F.R.S., &c. Received May 25. Read May 

 27, 1886. 



During the last two years, as opportunity has permitted, I have 

 been engaged in an experimental study of the various factors which 

 contribute to movement or rest of the small intestine. 



This research has furnished me with much information of an 

 analytical character, but it seemed desirable to supplement and, in 

 some degree, to control this, by investigating the general conditions 

 which influence such changes in a healthy animal in which all the 

 functions exerting an influence upon the viscera are in full operation. 

 The most promising means for effecting this purpose appeared to be 

 the establishing of a Vella's fistula which would permit of thorough 



