152 ANNUAL OF SCIENTIFIC DISCOVERY. 



CRAYON DAGUERREOTYPES. 



A VERY beautiful process for obtaining- crayon Daguerreotypes has 

 recently been discovered by Mr. Mayal, of London, formerly of Phil- 

 adelphia. This gentleman, refusing to take out a patent, has published 

 the process in the London Athenccum. It is as follows : Take a Da- 

 guerreotype image on a prepared plate as usual, taking care to mark 

 the end of the plate on which the head is produced. When taken, 

 and before mercurializing, remove the plate from the holder, and place 

 it on a plate of glass prepared as follows. Cut a piece of thin plate- 

 glass of the same size as the Daguerreotype plate, glue upon one side 

 of it a thin oval piece of blackened zinc, the centre of the oval to coin- 

 cide with that of the image upon the plate. Having carefully placed 

 the glass thus prepared, expose the whole to daylight, for twenty sec- 

 onds. The action of the light will obliterate all traces of the image 

 from every part of the plate, except that covered with the blackened 

 zinc, and also, from the thickness of the glass, the action will be re- 

 fracted under the edges of the zinc disk, and will soften into the dark 

 parts. Mercurialize the plate as usual ; the image will be found with 

 a halo of light around it gradually softening into the background, 

 that will at once add a new charm to these interesting productions. 

 By grinding the glass on which the disk is fixed, and by altering the 

 shape and size of the disk, a variety of effects may be produced which 

 every ingenious operator can suggest for himself. 



New Way to obtain Grovps. A pleasing experiment may be per- 

 formed, by covering successively different portions of the Daguerreo- 

 type plate, so as to exclude the operation of the light, except on that 

 portion of its surface required for the image. A group of any number 

 "of persons can thus be represented, each one being obtained at sepa- 

 rate sittings. The process is as follows: Take several pieces of 

 black paper, each paper having an opening, so arranged that no two 

 will expose the same part of the plate to the operation of light. Coat 

 the plate as usual, place one paper in the holder, over the surface of 

 the plate, and obsarve that the representation in the camera corresponds 

 in position upon the ground glass with that of the aperture in the pa- 

 per. When one impression has been taken, the plate should be kept 

 in the dark, and not exposed to the vapors of mercury until all the 

 desired impressions have been obtained. At each sitting, the paper 

 must be changed, and there is no difficulty in producing likenesses of 

 several persons on the same plate, each without the knowledge of the 

 others having ever sat. In this way the most ludicrous contrast of 

 individual appearances may be produced, as, for instance, of an old 

 maid and a young fop. Dagmrrcan Journal. 



NEW THERMOMETRIC SCALE. 



MR. S. M. DRACH, of London, has recently published an account 

 of a superior thermometric scale invented by himself. The prominent 

 feature of this plan is, that no negative degrees arc 7icccssary, except 

 for some chemical purposes and extraordinary arctic temperatures. 



