400 



♦ KNOWLEDGE ♦ 



[March 10, 1882L 



securo f,'oo(I inoriilioiml work, tlio astronoinor recognises in 

 him 11 ffllow-workcr. Ho says, with tho poet : — 



I nni na olil na G^rypt to niysolf, 



llrutlior to tlioin tlint Kiuarod tlio Pyrnniida : 



Uy tlio same sturs I watcli. 



And now consider whnt was tliis great ohscrvntory of 

 ancient l-^ypt — tho most perfect ever made till telescopic 

 art revealed a way of exact observation without those 

 massive structures. A iniglity mass, having a Imse larger 

 than the siiuarc of Lincoln's Inn, rising l>y just (ifty layers 

 to a height of about 112 feet, and presenting towards the 

 south the appearance shown in Fig. 1, where the mouth of 

 the (Jreat Gallery is seen opening southwards, and the lines 

 are shown which have been already indicated as "observing 

 directions" in the picture on p. .'il"). The Pyramid ob.serva- 

 tory is shown in section ii\ Fig. 2. It will be noticed that 

 the successive layers are not of equal thickness. There 

 arc just fifty between the base and plane of the floor of the 

 Kings Chamber. The direction lines for the mid-day sun 

 at midsummer, midwinter, and the equinoxes are shown ; 

 also the lines to the two stars, Alj)ha Draconis and Alpha 

 Centauri, are given at the subpolar meridional passage of 

 the former and the meridional passage of the latter, at the 

 date when the descending and ascending passages thus com- 

 manded both these stars. Within fifty years or so on either 

 side of this date, tho Pyramid must, I should think, have 

 been built. The later date when Alpha Draconis was at 

 the right distance from the Pole, 2170 d.c.,* is absolutely 

 rejected by Egyptologists — not one being ready to admit 

 that tlie date of the Pyramid King can have been any- 

 where near so lat?. 



PHOTOGRAPHY FOR AMATEURS. 



By A. BuoTUERs, F.RA.S. 



AMONGST the readers of Knowledge must be a large 

 number to wliora the production of a photograph 

 is a mystery, and there must be many who desire informa- 

 tion which would eiialjle them with little trouble and 

 expense to become so far expert, that although in some 

 respects the mystery will be as great as ever, they may 

 practice the art with some success. 



Less than fifty years ago, the only means we had for 

 recording the appearance of natural objects was by draw- 

 ing by hand, assisted in some cases by the camera hicida, 

 an instrument which cnabUxl the artist to have a correct 

 outline of the object, whether portrait or landscape, but 

 all detail of light and shade had to be filled in by hand in 

 the ordinary waj'. The black piofilo portrait, or siUwuclle, 

 is an example of what the photographer has superseded. 



It is proposed, in a series of short papers, to give an 

 outline of the history of photography, and details of some 

 of the processes which will be sufficient to enable anyone 



• Some may bo disposed to reject a cliann:o wliich they may 

 imagine displaces the Pleiades from the position wlucli Professor 

 Piuzzi Smyth assigned to that interesting group at tho date when 

 ho snpposcd tho Pyramid was built. But there never was the least 

 real significnnco in that position. If the mistaken idea entertained 

 by many, and repeated by Flammarion, Haliburton, and others, 

 tliat the Pleiades at their meridian shone down tho Great Gallery at 

 the Very time when the Pole Star of 2170 n.c. shone down the 

 descending Gallery, had been con-ect, there might have been some 

 reason to bo struck by tho coincidence. But it should hardly be 

 necessary to tell tho reader what every astronomer knows, that the 

 Pleiades never did or could shino dmvn tho Great Gallery, and in 

 tlio year 2170 B.C. were thirty-eight degrees (!) north of that posi- 

 tion. 



to take negatives and to print from them. It must bo 

 remembered, however, tliot, although the processes aro 

 not dirticult to master, some care and skill are required if 

 tho results an; to be of any artistic value. 



Without going dci'ply into the hi.story of the subject, it 

 will be suflicient to say thot one of the clicmical substances 

 now commonly used in photography was known in the 

 sixteenth century, and an alchemi.st, named Fabricius, 

 found that luna rorneti, as chloride of silver wa.s then 

 called, was so aff"ccted by light that an image produced by 

 a lens bi^came improved in light and shade on the surface 

 prepared with the iuna corwu. This must be considered 

 as the first discovery of photography, but the discoverer 

 failed to see the importance of it, and it was not until nearly 

 two centuries had elapsed that the curious effect caused by 

 light on the chloride of silver was re-discovered by Scheele 

 in 1777. This cliemist also failed to see the value of what 

 he had observed, and it was not until 1 802 that experi- 

 ments were made at all analagoi:s to what we now call 

 photography. In the year last-named, Tliomas Wedgwood, 

 assisted l>y Sir H. Davy, produced pictures on white 

 leather and paper, but, as no means were known by which 

 the images could be fixed, none of these early photographs 

 exist. 



The process of photographic printing now in universal 

 use, is based on these early experiments of Wedgwood and 

 Davy, and it may be interesting to repeat an experiment, 

 to show what kind of pictures they produced. Take a 

 piece of smooth writing-paper, float it in a solution of 

 common table salt (sodium chloride) for a minute or two, 

 then hang it up to dry, or dry it by tlie fire. When dry, 

 float the paper on a solution of silver nitrate, say 30 

 grains to the ounce of water (rain or distilled water sliould 

 be used), or the silver solution may be evenly bru.shed over 

 the surface with a large camers-hair brush, or by means of^^ 

 a glass rod, so as to avoid using a large quantity of silver 

 solution to float the paper upon. The prepared paperl 

 may be dried by the tire, or liung up in a darkene 

 room or cupboard. When quite dry, a leaf, piece of 

 lace, or any other suitable object may be placed on I 

 the paper, then covered with a piece of glass to) 

 keep paper and object in close contact, and then] 

 placed in sunlight. As soon as the paper is com-i 

 pletely blackened it will be found that the picture ofl 

 the leaf or other object will be printed on the paper as 

 negative — that is, the dark parts will be white, and rice] 

 versa. The paper still remains sensitive to light, and, of I 

 course, must be viewed only by weak daylight or byl 

 artificial light. This, then, is the reason why the earliest! 

 pihotogi-aphs are not now in existence. Later, those pholo-l 

 gallic Jraviiu/s, as they were termed, were immersed in| 

 plain water, by which the silver salt was partially remov.d.i 

 but the pictures were not properly fixed, and th» i 

 were not permanent. In a future paper we shall ser i 

 perfect fixation is efTected. 



We have no record of advance in photography until 1814, 

 when J. Niccphose, or Niepce, succeeded in producing per- 

 manent figures in bitumen of Juda?a ; the time required 

 rendered this process impracticable. About this time, and 

 leading up to 1839, Daguerre was engaged in researches 

 which resulted in the discovery of the process which bears 

 his name ; and this process for many years was most ex- 

 tensi\ely used, and the pictures produced remain to attest 

 the beauty and value of tho method. Daguerrotypes are 

 permanent if protected from the atmosphere, which tar- 

 nishes the silver surface on which the pictures are pro- 

 duced. This tarnish, however, can be removed by chemical 

 means, and the picture remains on the surface as perfect V\ 

 ever. ' 



