Daguerreotypists generally mark time by their watches, arriving at the nearest possible period for producing a good picture by making several trials. As a ready method of marking short intervals of time is, however, a very important consideration, and as any instrument which will enable an artist to arrive at the exact period, must be an improvement, and worthy of universal adoption, I will here describe one invented by Mr. Constable of England, which he calls a

Sand Clock, or Time Keeper.--"It consists of a glass tube, about twelve inches long, by one in diameter, half filled with fine sand, similar to that used for the ordinary minute glasses, and, like them, it has a diaphram, with a small hole in the centre through which the sand runs. The tube is attached to a board which revolves on a centre pin; on the side is a graduated scale, divided into half seconds; the tube is also provided with a moveable index. This instrument is attached, in a conspicuous place, to the wall. The glass tube being revolved on its centre, the index is set to the number of half seconds required, and the sand running down, the required time is marked without the possibility of error. In practice it will be found to be a far more convenient instrument for the purpose than either a clock or a seconds watch, and is applicable both for the camera and mercury box."

If the artist finds it desirable or necessary to take the object to be copied in its right position, that is reverse the image on the spectrum, he can do so by attaching a mirror (which may be had of Mr. Anthony, or Mr. Roach) to the camera tube, at an angle of forty-five degrees.

If, after taking the plate from the camera, it be examined, no picture will yet be visible, but this is brought about by the

FOURTH PROCESS.--Bringing out the Picture, or rendering it Visible.--We now come to the use of the mercury bath, Fig. 11. To the bath a thermometer is attached, to indicate the proper degree of beat required, which should never be raised above 170 deg. Fahrenheit. The plate maybe put into one of the frames (see Fig. 11,) over the mercury, face downwards, and examined from time to time, by simply raising it with the fingers, or a pair of plyers. This operation, as well as the others, should take place in the dark closet.

Fig. 26 (HIPHO_26.jpg)

[Updater's note: HIPHO_26.jpg and hipho27.jpg are both captioned Figure 27.]

Sometimes, to prevent the necessity of raising the plate, an additional cover or top is made use of. It consists of a box fitted closely to the inner rim of the bath, and having an inclined top (a, Fig. 27.) The top is cut through and fitted with frames for each size of plate, like those already described, and in the back is a piece of glass (b,) through which to view the progress of mercurialization, and an additional piece (c,) on one side, colored yellow, to admit the light. The outline only of the top is here given, in order to show every portion of it at one view.

The picture, being fully developed, is now taken out and examined; it must not, however, be exposed to too strong a light. If any glaring defects be perceived, it is better not to proceed with it, but place it on one side to be re-polished; if, on the contrary, it appears perfect, you may advance to the

FIFTH OPERATION.--Fixing the Image so that the light can no longer act upon it.--The following articles are required for this purpose:

Two or three porcelain or glass dishes, in form, something like fig. 24.

A plate support, fig. 25. Few, I believe, now make use of this, although it is a very convenient article.

Hyposulphite of Soda,

A pair of Plyers.

In Europe, they also use a drying apparatus, Fig. 27, but this, like the plate support, is a matter of little consequence, and may be dispensed with. I will, however, describe it, for the benefit of those who may wish to use it.

Fig. 27 (HIPHO_27.jpg)

[Updater's note: HIPHO_26.jpg and hipho27.jpg are both captioned Figure 27.]

A vessel made of copper or brass, tinned inside, and large enough to take in the largest plate, but not more than half an inch wide, is the most convenient. It must be kept perfectly clean. Hot distilled water is poured into it, and the temperature kept up by a spirit lamp.

Hyposulphite of Soda.--Having made a solution of hyposulphite of soda, and well filtered it--the strength is immaterial; about half an ounce of the salt to a pint of distilled water is sufficient--pour it into one of the porcelain dishes, put into another plain, and into a third distilled water. Immerse the plate with its face downwards into the hyposulphite, and the whole of the sensitive is removed, and the light has no farther action upon it; it is then to be removed from the hyposulphite and plunged into the plain water, or placed upon the support, fig. 25, and the water poured over it. It is then washed in a similar manner with the distilled water and well examined, to see that not the slightest particle of dust rests on the surface. The next step is to dry it.