Intelligence and Miscellnneons Articles. 54 1 



miles In the other ; it then in both becomes accelerated, and attains 

 to about seventy-six miles per hour. 



Lastly, the author observes that the node or hinge of the tide, 

 placed by Professor Whewell (in his papers on the Tides) in the 

 North Sea, is situated at the same distance nearly from the head of 

 the tide off Dungeness, as the node near Swanage is on the opposite 

 side of it ; and that in the Irish Channel, at the same distance nearly 

 as the node at Courtown is from the head of the tide off Peel, there 

 is a similar spot of no rise recently observed by Captain Robinson. 



The author concludes this paper by urging a further investigation 

 of the tidal i)henomena of the English Channel, on the ground of the 

 great advantage navigation, as well as science in general, would de- 

 rive from such an examination. 



Captain Beechey's letter is illustrated by twelve charts and dia- 

 grams, showing the identity and singular phenomena of these two 

 great channels. 



LXX. Intelligence and Miscellaneous Articles. 



ON THE ADVANTAGE OF ELECTllOTYPING DAGUERREOTYPE 

 PLATES. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 234 Regent Street, May 23, 1848. 



^I'^HE following simple experiment, demonstrating the advantages 

 ft of electrotyping Daguerreotype plates, may be interesting to 

 many of your readers, but more esjjecially to amateurs in that beau- 

 tiful art. 



Purity of silver for the plates has always been much insisted on ; 

 and of the various means that have been resorted to to obtain this, 

 the battery process offers the most simple as well as the most satis- 

 factory means of accomplishing it. 



Prepare a plate for silvering ; but in the place of depositing elec- 

 trotype silver over the whole face of the plate, only permit the de- 

 posit to take i)lace over one-half, by immersing the plate only half 

 way in the decomposition trough. [With a one quart Smee's battery, 

 one minute will be sufficient.] Finish the plate afterwards on re- 

 moving it from the battery in the usual way, as when preparing it 

 to receive the sensitive coating; and when "cross buffed," it will 

 be perceived, on examining the surface, how much blacker and more 

 brilliant is tlie jjolish on the electrotyped silver half, the remaining 

 half appearing by contrast quite greasy. The importance of this 

 depth of black will at once be ajjpreciated, when it is remembered 

 that it is the black burnish of the silver which forms the dark por- 

 tions or blacks of the Daguerreotyi)e picture. If the plate thus 

 ])repared be now made sensitive and placed in the camera, it will be 

 found that the electrotype half has also an adv.intage in sensitiveness, 

 the " halved image " being about four seconds, or about one-third 



