On ike Application of Photography to Diffraction. 251 



Composition of Nitric acid. Action of nitric acid 



Tvr„ o °^'- sp-gr. MOO. on the metals. 



i.>o. ^: — Loss. 



Cu . 10 eq. 77-77] Copper, most violent. 



Zn . 1 ... 14-23 L -Ofi T.-,f j„ 



14-23 ^ -06 Tin, do. 



Sn . 1 ... 8-OOj Zinc, do. 



No. 3 :— 



Cu . 4eq. 56-45\ 



Zn . 3 ... 43-55/ ^^ 



The results contained in the last table illustrate our views 

 completely, viz. that alloys having a definite composition offer a 

 most extraordmary resistance to the action of acids, as we have 

 alloys the metals of which are most violently attacked by nitric 

 acid, and still we find but a comparatively small amount of alloy 

 dissolved by this powerful acid. ^ 



We hope at a future time to publish the result of our labour 

 which will not only consist in examining the comparative tena- 

 city. Hardness, &c. of certain alloys, as compared with the metals 

 composing them, but the influence which, say one, two, or three 

 equiv-alents of a metal entering into the composition of an alloy 

 may have on the physical and chemical properties of the said alloy! 



^^7?/l' ?•" *^^ application of Photography to Experiments on 

 LondZ*''' Ti^^^OE, M.A. University College, 



TN addition to the difficulty of giving an explanation at once 

 "Ti- ff "f*^ ^"^ P«P'^lar «f the principles of the interference 

 ot light, the want of some cheap and convenient means of exhi- 

 bitmg Its phsenomena has hitherto prevented the subject from 

 being generally known. It is not my concern here to insist 

 that the former difficulty may be removed, but to describe a 

 means by which the phenomena may, at a trifling cost, be illus- 

 trated in as great variety as may be desired. 



If we look at a line of light through a series of equidistant 

 lines ruled on glass, lateral spectra are produced, whether a tele- 

 scope or only the naked eye be employed. Here is then an ex- 

 periment which may be performed in a simple manner; and to 

 make it a popular experiment, it is only necessary to produce 

 these lines cheaply. It occurred to me to do this by takin- a 

 collodion picture, as small as desired, of a series of lines rufed 

 on a scale as large as may be necessary to ensure accurate equi- 

 distance. When I had succeeded (to a considerable extent) in 

 this, .t seemed to me that by bringing the circles, triangles, or 



* Communicated by the Author. 

 S2 



