1844.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



40.5 



tiff, and yet press slightly on tlie speculum; the pressure being about one 

 pound for every circular superficial toot. The motions of tliis machine are 

 relatively so adjusted that the focal length of the speculum during the po- 

 lishing process, or tuivards the lateral end of it, shall he gradually becoming 

 slightly longer, and the figure will depend in a great measure upon the ra- 

 pidity with which this increase in the focal length takes place. It will be 

 evident that a surface, spherical originally, will cease to be so, if, while sub- 

 iecteJ to the action uf tlie polisher, it is in a continual state of transition 

 from a shorter to a longer focus ; in fact, during no instant of time will it be 

 actually spherical, but some curve, dilU'ritig a little from ihe sphere, and 

 which may be made to approach the [larabola, provided it be possible in 

 practice to give effect to certain conditions. An immense number of expei'i- 

 ments, wdiere the results were carefully registered, eventually established an 

 empirical formula, which affords at present very good practical results, and 

 may hereafter, perhaps, be considerbly improved. In fact, when the stroke 

 of the first eccentric is one-third the diameter uf the speculum, and that of 

 the secund eccentric is such as to produce a lateral motion of the bar which 

 moves the polisiier. measured on the edge of the tank, equal to "27, the dia- 

 meter of the speculum, or relerred to the centre of the polisher, of 17. the 

 figure will be nearly parabolic. The velocity and direction of tne motions 

 which produce the nece.'.sary Irictiun being adjusted in due proportion by the 

 arrangements of th? machine, and the temperature of the speculum being 

 kept uniform by the water in w hich it is immersed, there remains still other 

 conditions, which are essential to the production of the required result. The 

 process ot polishing ditfers very essentially from that of grinding: in the 

 latter, the powder emp'oyed runs loose between two hard surfaces, and may 

 produce scratches possibly equal in depth to the size of the particles; in tlie 

 polishing process the case is very different ; there the particles of the powder 

 lodge in the comparatively suft material of which the surface of the polishing 

 tool is formed, and as tbe portions projecting may bear a very small propor- 

 tion to the size of the particles themselves, the scratches necessarily will be 

 diminished in the same proportion. The particles are forced thus to imbed 

 themselves, in consequence of the extreme accuracy of contact bet« een the 

 surface of the polisher and the speculum. But as soon as this accurate con- 

 tact ceases, the polishing process becomes liut fine grinding. It is absolutely 

 necessary, therefore, to secure this accuracy of contact during tlie w hole pro- 

 cess. If the surface of a polisher, of consitlerable dimensions, is covered with 

 a thin coat uf pilclT, of sufficient hardness lo polish a true surface, however 

 accurately it may fit the speculum, it will very soon cease to do so, and the 

 operation will fail. The reason is this, that particles of the polishing powder 

 and abraded matter will collect in one place more than another, and as the 

 pitch is not clastic, close contact throughout the surfaces will cease. By em- 

 ploying a coat of pitch, thicker in proportion as the diameter of the specu- 

 lum is greater, there will be room for lateral expansion, and the prominence 

 can therefurc subside, and accurate contact still continue ; however, accuracy 

 of figuie IS thus, to a considerable extent, sacrificed. By thoroughly groov- 

 ing a surface of pitch, provision maybe made for lateral expansion cont:- 

 guous to the spot where the undue collection of polishing powder may have 

 taken place. But, in practice such grooves are inconvenient, being constantly 

 liable to fill up : this evil is entirely obviated by grooving the polisher itself, 

 and the smaller the portions of continuous surface, the thinner may be the 

 stratum of pilch. 



'•There is another condition, which is also important, that the pitchy sur- 

 face should be so hard as not to'yield and abrade the softer portions of the 

 metal faster than the harder. When the pitchy surface is unduly soft, this 

 defect is carried so far that even the structure of the metal is made apparent. 

 Whilst, therefore, it is essential that the surface in contact with the specu- 

 lum should be as hard as possible, consistent with its retaining the polishiu'"' 

 powder, it is proper that there should be a yielding where necessary, or con- 

 tact would not be preserved. Both conditions can be satisfied by formin" the 

 surface of two layers of resinous matter of difierent degrees of hardness ; the 

 first may be of common pitch, adjusted to the proper consistence by the ad- 

 dition of spirits of turpentine, or rosin ; and the other I prefer making of 

 rosin, spirits of turpentine, and wheat Hour, as hard as possible, consistent 

 with its holding the polishing powder. The thickness of each layer need not 

 be more than one-fortieth of an inch, provided no portion of continuous sur- 

 face exceeds half an inch in diameter, the hard resinous compound, alter it 

 has been thoroughly fused, can be reduced to powder, and thus easily ap- 

 plied to the polisher, and incorporated with the subjacent layer, by instan- 

 taneous exposure to fiame. A specidum of three feet diameter thus polished, 

 has resolved several of the nebulse, and in a considerable proportion of the 

 others has shown new stars, or some other new feature." 



In conclusion. Lord Kosse exhibited drawings of the nebulae, as figured by 

 Herschel, and also as they appeared in ihe telescope constructed by his Lord- 

 ship. 



Fig. 88 of Herschel, or 2 Messier, and 21 h. 2j ra. 5—1° 34' south, many 

 of the stars into which it is reduced by his telescope, are as large as those of 

 the first magnitude to the naked eye. 



Fig. 81, Herschel, the bright nebula nearflauri, figured by Herschel as 



perfectly elliptic and resolvable, but no stars seen, is seen in the telescope, 

 with three feet aperture, as a rather oval cluster of stars, with projeciing 

 filaments of stars ; some of these filaments exteniling considerably, so as to 

 give something of the idea of a scorpion. 



Fig. 29 of Herschel. The ring nebuia of Lyra, shows in the three feet 

 telescope, seven stars, one triple. It is an annular cluster, with fringes, and 

 the nebulous-looking centre in patches. 



Fig. 'B of Herschel, ;i planetary nebula, is also seen as an annular cluster. 



Fig. 26 of Herschel, the " Dumbell Nebula," is seen as an irregular cluster, 

 or raiher two in jiixta-position and nothing of the exact elliptic termination 

 of llerschel's figure. 



AMERICAN PATENTS. 

 (Frnm the American Journid o/ the Franklin Inslilute.) 

 I.MPROVED REV£I1BEB.\T0RT AND PUDDLING FUUNACES. 

 Specification of a Patent for " an improved reverheratory furnace far convert- 

 ing mineral, or ore. into iciougld-ironat tliefirst operation.'' Granted to.SiMEO.N 

 Beoadmuaeow, of Manayunk, Pennsylvania, and assigned to Wm. Green, 

 jun., of Woodbridge, New Jersey. — January 20, 1844. 



The new and improved reverberatory furnace is lor Ihe purpose ofdirectly 

 converting mineral, or ores of iron, into wrought-iron, ;.t the first operation, 

 by the process of puddling, using either anthiaciie, bituminous coal, or other 

 fuel, for that purpose ; which furnace is also usid for the puddling of pig- 

 iron, or of iron in other states, which is lo be submitled to that process, and 

 likewise for the melting, or healing, of metals forvarious purposes. 



The improvement consists in the so constructing it as that the hearth of 

 the furn;ice shall be heated both on its under and upper sides. For this pur- 

 piose a fire chamber is constructed, in which the fuel rests upon grate bars 

 directly under the hearth of the puddling furnace, there being an ash pit 

 under said grate bars, such fire chamber and ash pit being in the ordinary 

 form. The direct heat of the burning fuel which is contained in the fire 

 chamber, is, consequently, made to operate on the under side of the hearth, 

 and the heated air and flame ascend through a due space at the rear end of 

 the fire chamber, then along the puddling compartment, to the front of the 

 furnace, and thence back along a flue over the roof thereof leading to the 

 chimney, which is to be elevated in the ordinary manner to create a sufficient 

 draught.! 



Fig. I, 



Fig. 2. 



Scale, one-eigtlth of an inch to a foot. 



In Ihe accompanying drawing, fig. 1, is a front elevation of the furnace ; 

 the masonry which encloses it, and the chimney being omitted for the pur- 

 pose of showing the outline of the] interior. Fig. 2, is a vertical section 



35 



