316 Intelligence and Miscellaneous Articles. 



experiments show in a very striking manner the occurrence of the 

 extra current in the circuit of the battery itself, and are not less con- 

 clusive than previous experiments of the author on the heating of the 

 branches. — Monatsbericht der Berliner Akademie November 1863. 



" NEW BRITISH MINERAL. 



To Br, Francis, F.L.S. %c. 

 Dear Sir, British Museum, March 16, 1864. 



Would you do me the favour to find a corner in the April Number 

 of the Philosophical Magazine for the announcement that I have got 

 a new mineral from Cornwall, prismatic in crystalline form, and con- 

 sisting probably of a basic sulphate of copper insoluble in water ? It 

 occurs in minute but brilliant crystals ; and, in fine masses of the 

 richest blue colour, it forms a thick incrustation upon a tender killas. 

 It came to the Museum from Mr. Tailing of Lostwithiel, and I 

 shall give a more exact description of it in an early Number of the 

 Philosophical Magazine. 



I am, dear Sir, 



• Truly yours, 

 N. S. Maskelyne. 



NEW INVESTIGATION ON THE POSITION OF THE OPTIC CENTRE OF 

 THE EYE, AND DETERMINATION OF THE REFRACTIVE VALUES 

 OF THE DIFFERENT MEDIA. BY M. GIRARD-TEULON. 



I. By means of experiments, the object of which recalls those of' 

 Haldat, but in which I have modified (1) the direction of the light, 

 to which, by reflexion from a plane mirror at an angle of 45*, I im- 

 parted an upward vertical direction, and (2) the method of observa- 

 tion, inasmuch as I examined the images formed on the posterior 

 surface by means of the microscope, I obtained the following results. 



1 . Measuring the distance of the images at the anterior surface 

 of the cornea for parallel rays, and then their distance when the 

 object was brought within two inches of the eye, that is, at the two 

 extreme limits of accommodation, I found, in opposition to the facts 

 announced by Haldat, that during this motion of the object from 

 the horizon to two inches from the eye the place of the images 

 receded — 



In the ox, about 6 millims ; in the sheep, about 4 millims. ; 

 in the pig, about 3 millims. ; in the human subject, about 2*5 to 3 

 millims. 



2. Repeating these experiments with the eye deprived of cornea 

 and of aqueous humour, the results were virtually the same. It 

 appeared well established that the rays which fall on the crystalline 

 in the air, and those proceeding from the same and which meet it 

 after having undergone the refracting effect of the aqueous humour 

 and of the cornea, form a focus at the same distance from the poste- 

 rior face of the crystalline. (This fact had been already announced 

 by Haldat.) 



3. The crystalline being placed isolated in the air, the differences, 



