46 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[Jan. 21, 



diameter of the speculum ; it is produced by an eccentric fork. A fourth 

 motion takes place by the grinding disk, while for an instant free of the ring, 

 at the turn of the eccentrics, being carried round a little by the speculum, 

 on which it is then lying as it were free ; this causes it to turn once for 

 about 15 turns of the speculum. Emery and water being constantly sup- 

 plied, the surfaces of the grinding disk and speculum in a few hours grind 

 each other truly spherical, whatever be their original defects of form. The 

 process is finished, when, upou drawing oft' the grinding disk with one steady 

 long pull, the surface of the speculum is left everywhere uniformly covered 

 with the hue emery arranged in uniform lines, parallel to the line in which 

 the disk was drawn oft'. A slight polish beiug now given to the speculum, 

 its focal length is tested by a very simple process. The floors of the loft 

 above the workshop, in the tower of the castle, contain trap-doors, which are 

 now opened, and a mast erected on the top of the tower, which carries at its 

 top a short cross-arm, to the under surface of which a watch-dial is fastened, 

 the face of the dial looking down on the speculum, now directly under it, 

 and at a distance of 97ft. A temporary eye-piece erected in the upper floor 

 of the tower, soon finds the place of the faint and still imperfect image of the 

 watch-dial, the proper place of which is a matter of simple calcidation, if the 

 speculum be ground to the expected focus. If it be found incorrect, the 

 grinding disk is rendered a bttle more fiat, or a little more convex, and the 

 griuding process is renewed, and so on, until the spherical face of the speculum 

 is given its proper length of radius. When this is accomplished, the briUiant 

 reflecting surface, and true form for producing a good image, is given to the 

 speculum by the final process of 



Polishing. — In this, two matters require attention, the polishing powder 

 and the surface of the polisher. The powder used by Lord Rosse is not putty 

 or oxide of tin, as used by Newton and his followers, but red oxide of iron 

 procured by precipitation from green vitriol or sulphate of irou by water of 

 ammonia; this is to be heated carefully in an iron crucible, for it has a ten- 

 dency to take fire, and thus run many particles into one, and render the 

 polishing powder too coarse. The surface of the polisher used by Newton was 

 pitch in a very thin layer. Instead of pitch, which Lord Rosse found too 

 full of gritty impurities, he uses resin tempered with spirit of turpentine. A 

 large quantity of resin being melted, the spirit of turpentine is poured in, 

 and well mixed and incorporated (about a fifth by weight suftices.) The 

 proper temper is known by taking up a little on an iron rod, and putting it 

 into the water until it acquires the temperature, say of 55'^ Fahrenheit. Then 

 if the thumb nail make a slight but decided impression, it is rightly tem- 

 pered ; if not, more resin or more spuit of turpentine is added, until the 

 proper temper is attained. The tempered resin is now divided into two 

 parcels : to the one parcel a fourth part (by weight) of wheaten flour is 

 added to give it tenacity and diminish its adhesiveness. This is incor- 

 porated by stirring until it becomes clear. To the other parcel an 

 equal weight of resin is added, which makes it very hard. Upou this, 

 when cooled to 55°, the nail will scarcely make an impression. The 

 grinding disk, with its spherical surface turned upwards, is now heated 

 by fire underneath, and the resin rendered tenacious by flour laid on with a 

 brush in a thin even coat about, 150" Fahrenheit. This "coat and the griuding 

 disk are then allowed to cool down to about 100' Fahrenheit, when a thin 

 coat of hard tempered resin is laid on as evenly and thin as possible. The 

 smooth ground concave speculum is now covered with a creamy coat of the 

 fine polishing powder and water, and the warm polishing surface turued down 

 upon it at about 80" Fahrenheit, when it soon takes the form of the speculum 

 as in a mould ; care must be taken not to put on the polishing plate too hot 

 for fear of cracking the speculum, which the inter])osed creamy polishing 

 powder helps to protect ; nor too cold, else it will not take the proper figure. 

 The grinding engine now gives the same motions to the polishing plate as 

 before, but its weight is much diminished by counterpoising it. The soft 

 tenacious coat below, and the grooves on the surface of the grinding disk, 

 permit the proper lateral expansion, while the hard outer coating retains its 

 form, and holds firmly embedded the particles of polishing powder. The 

 polishing now proceeds rapidly, and as soon as what is technically called the 

 black polish is attained, the defining power is judged of by examining the 

 minute divisions of the image of the watch dial under an eye-piece of high 

 power. The true form is known to be given as the polishing proceeds, if 

 the focal length slowly increases in a tabulated proportion to the time. The 

 six foot speculum it is expected will be finished after six hours' polishing. 



NOTES OF THE WEEK. 



The Wilkie statue in the National Gallery has been the subject of much 

 interest and much discussion, and very dift'erent opinions have been expressed 

 as to its merits, according to the standard by which it has been judged. It 

 is the same with Cbautrey's horse in Trafalgar Square ; those who look to 

 precedent and consider prancing horses as legitimate, condemn it as tame ; 

 those who maintain that it is unnatural to have a fixed statue in a prancing 

 attitude, praise the artist's skill in preserving jnopriety, at the same time that 

 the vigour and life-like character of the animal is so well expressed. Mr. 

 Joseph has represented WUkie as a young man in the act of sketching on 

 bis tablets some vivid idea which has struck him. An objection to the ex- 

 pression of the countenance has been found in the fact that it does not give 

 strongly enough the national harsh features which the painter possessed, and 

 Mr, Joseph has softened down. How far it is legitimate to do this, will, of [ 



course, be decided agreeably to the diflferent views different parties entertain. 

 Wilkie being represented standing by the trunk of a tree and draped in a 

 cloak, is considered by some as improper, as if the artist could not as well 

 be represented pursuing his labours in the open air as in bis studio, while it 

 is not unnatural to imagine him struck by one of those peasant groups, which 

 he has transferred to canvass, 'i'he whole figure and its details have been 

 minutely scanned, and even the way in which the crayon is held has been 

 the subject of criticism. Neither has the place in which the statue is put be- 

 tween without its commentators, its location among the umbrella takers awaken- 

 ing the ire of some. For our own part, we must confess that it appears in 

 some degree derogatory that the artist should be kept waiting at the porch, 

 instead of being admitted to the cella of the temple of art; but, alas ! such 

 are the sad necessities of that unfortunate building, the National Gallery. 

 If, indeed, the ground-floor could not without props support the weight of a 

 statue, bow could the safety of the upper stories be jeopardized. It is la- 

 mentable that every year brings to light fresh defects in connexion with this 

 ill-conceived structure. Taking the statue of Wilkie as a whole, and allowing 

 for the necessities of its position, we are much pleased with it. The merit 

 of Mr. Joseph cannot be contested, though a differeuce of opinion may exist 

 as to details of treatment, and as to the fact of the statue being erected, and 

 we are glad to take it with all its defects, as a first oft'ering to men of art in 

 the national building. If Willde is to be honoured, surely others cannot be 

 neglected, and we hail, therefore, with pleasure the prospect of a proper 

 commemoration of ancient individuals. If statues are awarded to painters 

 and sculptors, the honour of architecture cannot be forgotten, and we hope 

 to see the day when Wren, Inigo Jones, and Chambers will receive due 

 homage. 



The public works, which have been brought forward recently, seem almost 

 without exception to have met with strong support, and there is every pro- 

 bability of a great number of new railways being authorized in the ensuing 

 session. This wUl be a most seasonable relief to professional men, whose 

 employment has been so seriously interfered with by the restrictive legisla- 

 tive enactments. 



The basins for the fountains in Trafalgar Square have been asphalted. 

 The contract for paving the whole of the square has been taken by the Bas- 

 tenne Bitumen Company, who will proceed immediately to lay down their 

 composition. 



We are sorry to see that the foundations for the buildings in 'Change 

 Alley, or rather Freeman's Court, are being proceeded with. 



A new Concert Hall has been opened at Rotterdam from the designs of 

 Mr. W. N. Rose. 



The painter Ferdinand Deurer died at Munich on the 9th, aged 07. The 

 lithographer Piloty died in the same city on the 15th. He was one of the 

 oldest lithographers, having begun in 1808. 



The new English steamer for the Main Steam Navigation Company ar- 

 rived at Frankfort on the 9th. She made the passage in two hours less than 

 the old boats. 



The first steam towing boat for the Company of the Palatinate has been 

 launched at Strasburg. 



The works for the rebuilding of Hamburg get on well. At the end of 

 December, the bridges in the Gorttwiete, the Steintwiete, and of the Exchange 

 were finished, and in use. The quay on the Monkedamm is in active pro- 

 gress. The bridges over the Kastenschleuse and the Resendamm are begun. 

 At the last meeting of the magistrates for Middlesex on the 18th instant, 

 Mr. George Legg was elected district surveyor for the united parishes of St. 

 Andrew, Holborn, St. George the Maityr, and the Liberty of the Rolls. 



The Assize Court at Cambridge, designed by Wyatt and Brandon, is to be 

 decorated by a series of four colossal statues of Law, Power, Justice, and 

 Mercy. 



The Eastern Counties' contract for the Northern and Eastern extension is, 

 we understand, signed at about .£12,000 a mile, for everything. Grissell and 

 Peto are the contractors. 



Another large hotel, 150 feet larger than the present, will be begun at 

 Folkestone in the course of next month. 



Mr. Macqueen has brought out a voluminous pamphlet, which we have 

 had the good fortune to see, in which he enters most fully into the details 

 of the management or rather mismanagement of the Royal Mail Steam Na- 

 vigation Company. It is certain to make a great sensation, and we shall 

 take an early opportunity of entering into the subject. Mr. Macqueen's 

 vindication of himself seems complete ; as to his inculpatioa of other parties, 

 that must be matter of investigation. 



Another large work has been published at the expense of the Pope on the 

 Etruscan Museum Gregorianum ; it is in two volumes, and contains upwards 

 of 200 plates. 



Of DuramVs Paralle'le — one, however, not quite so well planned as it might 

 have been — a new edition has lately been brought out at Brussels, containing 

 a great many additional, and also several unedited subjects. Among them 

 are La Madeleine, Notre Dame de Lorette, L'Ecole des Beaux Arts, Le Palais 

 du (Juai d'Orsay, and several other recent monuments of Paris : further, the 

 University at Ghent, the Palace of the Grand-Duke Michael at St. Peters- 

 burg, the Royal Palace at Stockholm, some buddings in Germany, the Royal 

 Palace at Naples, and that at Madrid. Among them all, however, there is 

 not a single example of any of the numerous buildings erected in England 

 and Scotland within the present century. It would therefore seem that our 

 architecture is not held in greater esteem on the Continent, than foreign ar- 

 chitecture is by some bere at home. Or possibly, the omissiou may not so 



