102 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[April, 



ON THE COMBINATION OF THE TELESCOPE WITH 



THE DAGUERREOTYPE. 



{From the Transactions of the Royal Society of Bohemia, 1846.) 



Professor Doppler, of Praguo, says, that for the ascertaining of 

 the diameters of tixed stars, tlie telesjope has been hitherto mainly 

 depended upon, and that tht- instrument han been so far improved as 

 it possibly ever can and will. The susceptibility of the human eye 

 for the minutest objects has been hitherto consiilered paramount; but 

 M. DoppU-r asserts, tiiat the susceptibility of the human retina is 

 surpassed many thousand times by that of a prepared (iodized) Da- 

 guerreotype plate. Physiological experiments have shown, that ob- 

 jects, wliich appear to us under an angle of vision fcss than 50 or 40 

 inches, are no more seen nj cr/eHso, but as amorphous simple points. 

 On the other h and, physiological researches o( such men as Miiller, 

 Weber, &c., have shown, that the diameter of one of the nerve- 

 papillae of the retina is no more than -^^'^f^ or aTnnr of ^^Q ''"^'i- P^^> 

 comparing the susceptibility of the retina papillae with the micro- 

 scopic experiments made with Daguerre's plates, it will follow that 

 the single globules of mercury are of such extreme minuteness, that 

 they become only visible by a'SOO-fold magnifying power; and, tliere- 

 fore, that on the space of a D aguerre plate, equal to one retina papil- 

 la, more than 40,000 single minute globules of precipitated mercury 

 are to be met with. Each of these is capable ot producing the 

 image of well detined objects— which would merge on the human 

 retina in single, indiscernible luminary points. Thence, Prof. Dop- 

 pler argues, that Daguerre's plates are 40,000 times more susceptible 

 for impressions than the human eye. 



Considering, moreover, that a great improvement in microscopes is 

 very probable, M. Daguerre thinks that instead of telescopes,— micro- 

 scopes will come into use. At the exact point, therefore, where the 

 image of a celestial body is formed before the object-lens of a tele- 

 scope of considerable length, an apparatus is to be placed, whereby a 

 silver plate (iodized, brome-iodized, or otherwise prepared) can be 

 securely inserted. As the place of the images is the same for all 

 celestial objects, a plate of a well defined, constant thickness, can be 

 inserted with great accuracy. la this way, D.iguerreotype images of 

 all, even of the smallest, fixed stars can be obtained, if (as is to be 

 supposed) the light will be sufficient to atfect the plates. It is also to 

 be taken into account, that the images of the fixed stars, obtained by 

 an object-lens of from 10 to 12 inches, will possess a light, 10,000 

 times stronger than they present to the naked eye. Plates thus al- 

 fected, are to be treated with mercurial vapours and laved (tai);/-/ .<'), 

 and then viewed bv a good microscope. As these images will have 

 been magnified (through the action of an object-lens— say of 110 

 inches focus lenglh) to the extent of 14 times their natural appaar- 

 ance; and being again magnified 1,200-fold,— the angle of vision under 

 which they are now to be viewed, will have been increased lt5,S00- 

 fold. 



REVIEVtrS. 



Encyclopiedia of Civil Engineering, — Historical, Theoretical, and 



Practical. By tDWARD Crest. Royal Svo. London: Longman 



and Co. 1847. 



Mr. Cresv's long expected Encyclopedia of Engineering has at 

 length made its appearance, much to the credit of its indefatigable 

 and talented author, who after three years of compilation has produced 

 a work which forms a vast octavo volume, consisting of rather more 

 than IGOO closely printed pages, and upwards of 3000 well executed 

 wood engravings by Branston. 



The work is divided into two parts — the one entitled "The His- 

 tory," the other "The Theory and Practice, of Engineering." The 

 first division might with more propriety have been termed the "His- 

 tory of Engineering and Arcliit -cture," as a consider.ible portion of it 

 is devoted to the description i.f merely the external forms of edifices. 



To the History of Engineering we shall for the present confine our 

 rem.irks, reserving for another O|)portunity the consideration of the 

 second and more practical division. From this our aera of " the rail- 

 way and the steam-ship, and the tlioughts that shake mankind," 

 Mr. Cresy transports us to a period coeval with th.' first rude at- 

 tempts of/Etheopian architecture, and starting from that point ex- 

 hibits, step by step, the gr.ulual progress of structural science. The 

 principle of the arch, which, according to the authorities quoted in the 

 Encyclopaedia, must have been known to the early Egyptians, is lost 

 bight of in a marvellous manner by the Greeks; its employment even 



by the Egyptians, seems to have been very limited. The trabeate 

 was apparently more consonant than the arcuate style to the severity 

 of ancient ideas of beauty. The repose, the grand simplicitv, and 

 oneness of elTect of early Grecian architecture are due, mainly, to the 

 exclusion of .ill curved lines and tracery, and seem to us impossible to 

 be developed in any construction that admits the arch as a prominent 

 feature. For our part, we believe that the contrast between the vast 

 simple masses of ancient masonry, and the clear deep unclouded blue 

 of an eastern sky, must have produced an effect infinilelv more sub- 

 lime than the most gorgeous of English arcuate cathedrals, viewed as 

 thuj are against the clonded sky, and through the smoky medium of 

 our dull climate. The vault of Mycens, to which reference has been 

 made in a former number, is a curious instance of the form, without 

 the properties, of the arch. 



From Grecian, Mr. c;rpsy conducts us to Roman architecture, a 

 division of the work containing some highly interesting information, 

 of which we shall pr 'cei-d to give an analysis. It commences with an 

 account of the walls, towers, and other military defences of the im- 

 portant city of Rome: we have engravings of the wall of Sevrus 

 Tullius, which surrouu led the entire city ; the bold severity of the 

 outline, the battering of the lower portion of the wall, and the capping 

 formed by an einbattlement, show at once its object — that of a defen- 

 sive boundary ; — next we have the Aurelian Wall and Gate of St. Paul, 

 then the Gate of Spello, of Aosta, approaching in design to our Norman 

 style of architecture. The Gate of Perugia is another example of ao 

 early gate, marked by the boldness of its outline. The Gate of Augus- 

 tus, at Fano, is of a more ornamental character: — 



^3a 



THE GATE OP AHGUSTUS AT FANO. 



" The lower portions of which are of great antiquity. Farm u Fortunae was 

 the name the city formerly bore, which, from its saniptaous buildings, was 

 greatly admired. There are three entrances, fliuked by circular towers, 

 wliich rise to a considerable height, the two upper stories hiiuj lighted by 

 semicircular-headed openings, and crowned with a bald projijcting cornice, 

 over which is the hattleoieiit. Immediately over the three entrances was a 

 gallery, formed hy seven arches, between Corinthian pilasters, and surmounted 

 hy a regular entablature. The repairs these walls underwent during the 

 reign of Constantiue somewhat changed their character, and since that pe- 

 riod the upper story was destroyed by a cannonading which took place when 

 this town opposed Julius II. Various inscriptions remain amid the several 

 works of restoration." 



and lastlv, we have the Gate of Autun, one of a triumphal character. 



The work then proceeds describing the materials used in the edi- 

 fices of Rome. Burnt bricks came into general use for public build- 

 ings about the time of Augustus, when they were made less than an 

 inch in thickness, of u triangular shape ; sometimes the brickwork was 

 formed of a mixture of red and yellow brick ; at a later period a mixed 

 construction was formed of brick and tufa, as inCaralla's circus. With 

 the decline of Roman institutions, we are told that the art of construc- 

 tion lost its excellence, and that no care was taken in the selection of 



