Royal Society. 31 1 



perposed in such a manner that the dark and bright bands respect- 

 ively coincide. Thus distinct bands are visible in the secondary 

 spectrum, although none would be seen in the spectrum formed by 

 a single prism, in consequence of the mixture of the bright and dark 

 bands belonging to different kinds of light of nearly the same degree 

 of refrangibility. The diffraction bands here spoken of are of very 

 sensible breadth, in consequence of the small width of the aperture 

 employed in the actual experiment. 



When a spectrum is viewed through a narrow slit half covered by 

 a plate of mica, the edge of which bisects the slit longitudinally, and 

 is held parallel to the fixed lines of the spectrum, the bands described 

 by Sir David Brewster are seen, provided the mica plate lie at the 

 side at which the blue end of the spectrum is seen, and provided the 

 thickness of the plate and the breadth of the slit lie within certain 

 limits. When these bands are invisible in consequence of the slit 

 being too narrow, or the spectrum too broad, it follows from theory 

 that the bands ought to appear when the slit and plate are turned 

 round the axis of the eye, so that the edge of the plate is no longer 

 parallel to the fixed lines of the spectrum. The author has verified 

 this conclusion by experiment, employing plates adapted to obser- 

 vations with the naked eye, which are best suited to the purpose. 



Feb. 1. — "On the Chemistry of the Urine ;" in three Parts. By H. 

 Bence Jones, M.D., M.A., F.Il.S. 



Part I. On the variations of the Acidity of the Urine in Health. 



The mode of examination adopted by the author was the following : 

 Two test solutions were made ; the one with carbonate of soda ; the 

 other with dilute sulphuric acid, of such strength that each measure 

 of a graduated tube, when filled with either solution, was equivalent 

 to one-twelfth of a grain of dry and pure carbonate of soda. 



A weighed quantity of urine was neutralized by one or other of 

 the test solutions, and thus the degree of acidity or alkalescence was 

 determined. 



Diurnal variations in the acidity of the urine were observed. The 

 acidity of the urine was found to ebb and flow ; it was greatest a 

 short time before food was taken, and was least about three hours 

 after breakfast, and five or six hours after dinner, when it reached 

 the minimum point ; after which it again increased, and attained the 

 maximum point previous to food being again taken. 



If no food was taken, the acidity varied but slightly for twelve 

 hours. 



By comparing the effect of vegetable food with animal food, it 

 appeared that the food which irritated the stomach most and caused 

 most secretion of acid in the stomach, caused the greatest oscillations 

 in the urine. 



Dilute sulphuric acid taken in large doses produced but little 

 effect on the variations of the acidity of the urine ; but it was proved 

 to increase the acidity of the urine. 



Part II. On the simultaneous variations of the amount of Uric Acid 

 and the Acidity of the Urine in a healthy state. 



The result of these experiments is, that there is no relation be- 



