Intelligence and Miscellaneous Articles. 239 



taining dilute sulphuric acid, with which can be mixed substances 

 suitable for causing the capillary constant of the meniscus to vary — 

 such as chlorhydi'ic acid, chromic acid, &c. The electrical difference 

 of the meniscus can be maintained constant. Tor that purpose 

 the mercury and the liquid under experiment are put in communi- 

 cation respectively with some mercury and acidulated water con- 

 tained in a large vessel V. It can then be ascertained that the 

 changes in composition of the liquid V do not cause the position of 

 the meniscus to vary ; this can be verified by means of a microscope 

 with a reticule. If the electrica] communications described above 

 be suppressed, the meniscus becomes, on the contrary, very sensi- 

 tive to the changes of chemical composition of the liquid. 



It is necessary to employ for these experiments substances 

 which, in small quantities, act powerfully on the capillary constant; 

 two aqueous solutions put into contact do not take sensibly the 

 same electrical potential, unless they have nearly the same chemical 

 composition. Between two very different liquids, such as chlor- 

 hydric and sulphuric acids, taken each pure and diluted, an electro- 

 motive force of contact is produced, which would complicate the 

 experiment. As bodies active in small quantities we may mention 

 (1) the hydro-acids and hyposulphite of soda, and (2) bichromate 

 and permanganate of potash in the presence of acids. Chlorine, 

 sulphurous acid, and carbonic acid, on the contrary, have but little 

 action. Bromiue and iodine act in the same direction as the hy- 

 drogen acids, and in the opposite direction to the oxidizing bodies, 

 such as chromic acid. — Comptes Rendus de VAcademie des Sciences, 

 July 16, 1877, tome Ixxxv. pp. 142-144. 



NOTE ON THE EFFECT OF CHROMATIC ABEREATION IN DISTANT 

 VISION. BY B. THOMPSON LOWNE, F.R.C.S., ARRIS AND GALE 

 LECTURER ON ANATOMY AND PHYSIOLOGY IN THE ROYAL 

 COLLEGE OF SURGEONS, LECTURER ON PHYSIOLOGY IN THE 

 MIDDLESEX HOSPITAL MEDICAL SCHOOL, OPHTHALMIC SUR- 

 GEON TO THE GREAT NORTHERN HOSPITAL. 

 Mr. S. P. Thompson, in a communication on this subject published 

 in the July Part of the ' Philosophical Magazine ' speaks of chromatic 

 aberration as if it were an advantage in distant vision. I fail to 

 understand, however, how this can be the case. There can be no 

 doubt that distant objects are seen with a predominance of the 

 more refrangible blue and violet rays ; an eye, therefore, which is 

 emmetropic for such rays is hypermetropic for the less -refrangible 

 red rays. Taking the dispersive power of the eye as equal to that 

 of water, this hypermetropia amounts to two dioptrics. Such an 

 eye would therefore have the red objects of the foreground more 

 out of focus than if it were achromatic. An eye which is emme- 

 tropic for red would on the other hand have blue objects accurately 

 focused, without any accommodation, if they were situated at a dis- 

 tance of half a metre from the eye. No doubt, if red and blue are 

 situated on the same plane at the same distance from the eye, as 

 the red requires the greatest effort of accommodation it will appear 



