374 



Daguerreotypc- 



■Cast-iron Buildings. 



Vol. VII. 



by having' a guide made fast to the beam of 

 the plough, in which the beam of the Dyna- 

 mometer should play; the balance could then 

 be made fast to the upper slat or round of 

 the plough, and be more convenient lor ob- 

 servation ; and besides this, it would not be 

 affected by inequalities on the surface of the 

 ground." 



The thing certainly appears very feasible, 

 and I hope that some of your intelligent 

 readers will put it to the test of a careful 

 and rigid examination, and report upon it in 

 the pages of the Cabinet; its simplicity re- 

 commends it strongly to the notice of every 

 one of our agricultural friends, and it is a 

 subject that demands their most serious re- 

 gard, as being the only mode, in the absence 

 of the power of speech in our teams, by 

 which the tremendous difference which ex- 

 ists between the draughts of different ploughs, 

 can be exhibited or explained. C. W. 



Warren co., N.J. 



Our correspondent's remark reminds us of a late 

 conversation with Mr. H. Roberts, of Spring-Mill, 

 Montgomery count}', after a trial between the Centre- 

 draught plough and one of Dickinson's— the plough, it 

 will be remembered, that took the premium at the last 

 Philadelphia Agricultural Society's ploughing match: 

 He said, "the land at last got so hard that my small 

 horses could no longer work the Dickinson plough; my 

 brother, therefore, gave me the Centre-draught plough, 

 No. 5, and took the Dickinson, when my horses walked 

 away with it, almost as though they had nothing after 

 them: but when my brother started his strong team 

 with the Dickinson plough, they stopped and drew up, 

 as though they had met with an obstacle; nor would 

 they move it until they were urged." Here was a liv- 

 ing Dynamometer, that spoke the truth, without the 

 possibility of any mistake. J. P. 



Daguerreotype. 



The following is a general description of 

 the art of the Daguerreotype, as practised 

 by its distinguished inventor: A plate of 

 silvered copper, after having been well 

 cleaned, and freed from any greasy sub- 

 stance, by polishing it with dilute nitric 

 acid, line tripoli, or colcothar of vitriol, is 

 placed in a box containing iodine, till its 

 surface is covered with a golden yellow 

 film of that evaporable substance. The 

 plate being carefully kept from light, is 

 placed in the camera obscura, so as to re- 

 ceive upon its surface a distinct image of 

 the landscape, or of the single figure, or 

 group of figures, to be painted. After re- 

 maining a number of minutes, depending 

 on the intensity of the light, the plate is 

 taken out of the camera, and placed in what 

 is called a mercury box. There it is exposed 

 to the vapour of mercury, raised by a spirit 



lamp; and after a certain time, the operator, 

 looking through a little window in front of 

 the box, observes the landscape, or figures, 

 gradually developing themselves on the sur- 

 face of the plate, by the adhesion of the 

 white mercurial vapour to those parts of the 

 picture which had been acted upon by the 

 light. When the developement appears 

 complete, the plate is placed in a vessel 

 containing either a saturated solution of 

 common salt, or a weak solution of the hy- 

 posulphite of pure soda. By the action of 

 either of these fluids, the coat of iodine is 

 dissolved, and the picture is permanently 

 fixed. It is then simply washed in distilled 

 water, — dried, and placed in a square of 

 strong pasteboard, covered with glass. If 

 we now carefully examine the picture thus 

 produced, we shall find that its shadows are 

 nothing more than the original polished sur- 

 face of the silver, reflecting a dark ground, 

 and that the lights are the parts of the sil- 

 vered surface, which have been more or less 

 whitened by the vapour of mercury. If the 

 plate is made to reflect a luminous surface, 

 such as a white dress, or the sky, the sha- 

 dows will appear luminous and white, and 

 the lights dark, so as to give what may be 

 called a negative picture. In this remark- 

 able representation of nature, there is de- 

 picted, with the minutest accuracy, all her 

 finest forms; but her gay colours are want- 

 ing; and the blue sky, and the green turf 

 are exhibited in the same monotony of light 

 and shadow, as when we view a highly co- 

 loured land.^cape, in water colours, or in oil, 

 by the light of a monochromatic lamp. — Ed- 

 inburgh Review, Jan., 1843. 



Cast-iron Buildings. 



We take the following from the January number of 

 the Journal of the Franklin Institute. 



"A correspondent of the Times, says: — ■ 

 Build inns of cast-iron are daily increasing, 

 at a prodigious rate in England, and it ap- 

 pears that houses are about to be constructed 

 of this material. It is proposed that the walls 

 shall be hollow, so that the whole house may 

 be heated by a single stove in the kitchen. 

 A three-story house, containing 10 or 12 

 rooms, will only cost about £1000; and it 

 may be taken to pieces, and removed to an- 

 other place, at an expense of about £25. It 

 is understood that a large number are about 

 to be manufactured, to be sent to Hamburg, 

 for those who have had their habitations 

 burned." 



A heart properly disciplined, will enable 

 the head to accommodate itself to whatever 

 pillow the vicissitudes of fortune may place 

 under it. 



