1898.] Messrs Heycock & Neville, Rontr/en photographs. 417 



(3) Rontgen photographs of metallic alloys. By Mr G. T 

 Heycock and Mr F. H. Neville. 



The authors exhibited aud described photographs taken by 

 means of the Rontgen rays through plates of alloy. As the two 

 metals forming the alloy possess different degrees of transparency 

 to these rays the photographs show the separation of the metals 

 that has taken place during the solidification of the alloy. For 

 example, alloys of gold and sodium containing less than 30 per 

 cent, of gold are seen to consist of well-developed, very transparent 

 crystals, which must be pure or nearly pure sodium, imbedded in 

 a mother substance which solidified last, and which from its com- 

 parative opacity evidently contains the gold. On the other hand, 

 alloys containing more gold show very opaque needles of gold im- 

 bedded in a less opaque mother substance. This mother substance 

 was the same as that in the first-mentioned alloy ; it solidified 

 after the needles of gold had been formed. Photographs of alloys 

 of aluminium and gold and of aluminium and copper were shown 

 which exhibited similar phenomena. The crystals of aluminium 

 in the alloy with copper were perfect rectangular crosses several 

 millimetres in diameter. The gold-aluminium alloys showed a 

 precipitate of Roberts-Austen's compound of the formula AuAU ; 

 the crystals were well-marked cubes and octahedra. 



Monday, 7 March, 1898. 

 Professor Newton, Vice-President, in the Chair. 



The following Communications were made to the Society : — 



The Coral Reefs of Funafuti, Rotuma and Fiji together with 

 some Notes on the Structure and Formation of Coral Reefs in 

 general. By J. Stanley Gardiner, M.A., Gonville and Cains 

 College, Cambridge. 



INTRODUCTION. 



Having been enabled by means of a grant from the "Balfour 

 Fund" to join the "Coral Reef Boring Expedition" to Funafuti, 

 I had the pleasure of spending upwards of three months on 

 that atoll with Prof. 'Sollas, who suggested to me the propriety of 

 comparing its reefs with those of Fiji and other islands in the 

 vicinity. To Prof. Sollas 1 am under deep obligations, and any 

 value that my observations may have is largely due to him. 



