570 



• KNOWL.EDGE • 



[May 5, 1882. 



is detenniiied by the size of the glass used. The de- 

 veloping solution must be caused to flow evenly over the 

 plate by pouring it on at the lower edge, and at the same 

 time by so accommodating the position of the plate that 

 the solution will flow in one sweep to the top, and care 

 should be taken to allow as little as possible to run ofl'. 

 The reason for this is that the silver is required to form the 

 picture, and if waslied away the image may be weak. If 

 the proper exposure has been made, the image will soon 

 appear, and its development must be carefully watched, in 

 order to avoid too much intensity. Tlie solution must be 

 kept in gentle motion whih; on the plate, and may be 

 returned to the glass cup while the plate is examined, and if 

 the development has not been sufficient, it must be again 

 poured on. Experience alone can determine this, and it will 

 quickly be gained. What is required is sufficient intensity 

 to give the proper light and shade in the ]}rint on paper, 

 which is the object in view in taking the negative. 

 Usually, when iron is used as the developing agent, the 

 image is not sufficiently dense for printing from, and, when 

 this is the case, it must be intensified. The solution for 

 this must contain 15 grains of pyrogallic acid, 5 grains of 

 citric acid, and water .5 ounces ; and it is used by taking 

 sufficient of the solution to cover the plate and a few drops 

 of silver solution (20 grains, for water 1 ounce). This is 

 used in the same way as the developing solution, and the 

 effect on the negative must be watched to avoid over- 

 intensity. After use, the developing and intensifying 

 solutions may be put into any convenient receptacle when 

 the silver they contain may be recovered in a metallic state. 

 The negative image is still veiled by the unreduced 

 iodide of sUver, and this can be removed by pouring over 

 the plate a weak solution of potassium cyanide which will 

 clear the plate, leaving only the metallic image. As 

 potassium cyanide is a dangerous poison, hyposulphite of 

 soda is preferred by some operators ; its action is not so 

 energetic as cyanide, but it answers the purpose equally 

 well. A saturated solution should be used — that is, suffi- 

 cient of the hyposulphite of soda must be put into the 

 water until it will dissolve no more, the surplus crystals 

 may remain in the bottle, and the solution may be re- 

 peatedly used. 



The negative must be carefully washed after each of the 

 (^orations we have now described, and if hyposulphite of 

 soda be used for fixing, the washing must be more 

 thorough than when cyanide is used. 



If allowed to dry spontaneously, the plate must be 

 turned face to the wall, or it may be at once dried over a 

 spirit lamp, or by a fire ; care being taken to avoid dust. 

 In the experimental stage, the negatives need not be var- 

 nished before they are printed from. Before varnishing, 

 make the negative so hot that it is just bearable when 

 touched on the back of the hand, then pour on varnish as 

 if it were collodion, returning surplus to stock bottle. Dry 

 by fire, and the negative is complete. 



The Imperial Commission of German Scientists, who will come 

 to America to observe the transit of Venus on Dec. 6 next, will 

 establish posts of observation in Cliaileston, S.C, and in Hartford, 

 Conn. The Lepslaturo of the latter State has adopted a resolution 

 extending its courtesies to the distinguished visitors, and granting 

 permission to erect on the State Capitol grounds a temporary 

 building for their scientific apparatus. 



A NATURALIST says there is au "ant town" in the Alleghany 

 Mountains. It consists of sixteen or seventeen hundred nests, 

 which rise in cones to a height of from two to five feet. Thegroand 

 below is riddled in every direction with subterranean passages of 

 communication. The inhabitaiits arc all on the most friendly 

 terms, so that if any one nest is injured, it is repaired by help 

 from the other nests. Foreign auts of the same species are not 

 tolerated. 



HANLAN AND TRICKETT. 



By an Old Club Captain. 



I WAS able to study the action of these two scullers 

 under favourable conditions on Monday, hoping to find 

 evidence Vjearing on the question of rowing styles. But 

 the superiority of Hanlan was manifestly not due entirely, 

 or even chiefly, to any differences such as I touched on in 

 my discussion of the styles in vogue at the two Universities. 

 Yet the characteristic feature of Hanlau's rowing illus- 

 trates the principles I then considered. This feature is 

 his marvellously scientific method of sliding ; for he so uses 

 the slide as to combine the effect of slide, swing, and arm 

 work, thus bringing arms, back, loins, and legs into simul- 

 taneous action, so that his boat seems as if driven from 

 a catapult. Then, so perfectly is each stroke given that 

 there is not the slightest perceptible dip, and therefore no 

 force lost in vertical pressures, and as little loss of way as 

 possible between the strokes. One feature in Ilanlan's build 

 surprised me. I had been told that his muscular develop- 

 ment is singularly well-proportioned, that there is no 

 abnormal or unusual show of any muscles, but that all the 

 principal muscles of the body are well developed. Also 

 when I met him at Toronto, I had failed to recognise 

 the peculiarity to which I now advert — viz., a most ab- 

 normal development of the deltoid, as compared with 

 the biceps muscles. I venture to say that Hanlan is an 

 anatomical marvel in this respect. 



THE NAVAL AND SUBMARINE 

 EXHIBITION. 



THIS exhibition, which formed one of a couiov- ^1 what 

 may be called " trade exhibitions," at the Agri- 

 cultural Hall, Islington, and which has been held during 

 this month, was, in the opinion of those old enough and 

 able to judge, by far the best of its kind which has taken 

 place since the Great Exhibition of 1862. Certain it is 

 that the processes and appliances exhibited by some 500 

 or 600 firms are fraught with extremely great interest, 

 not only to those in the various trades represented, but 

 also to the general public. It is doubtful if anything can 

 be conceived of greater importance than the saving of life 

 at sea. Numerous systems having this object in view were 

 offered to the public, embracing life-buoys, belts, boats, 

 lie, and in addition to the ordinary boats, there were to be 

 seen a number of devices, more or less ingenious, for com- 

 pactly showing such vessels, yet in such a manner that 

 they could be lowered in an almost inappreciably small 

 space of time — time, in fact, which could be counted by 

 seconds. In one case, the boat, made of canvas-like mate- 

 rial, itc, could be doubled up longitudinally, and placed 

 by the side of a ship, occupying only a fifth of the space 

 it would till when laid open. There were also several 

 arrangements for releasing the boats from the davits, the 

 best, perhaps, being that which allowed the hooks to drop 

 away as soon as the boat touched the water. 



Diving apparatus occupied a very prominent place ; the 

 most important exhibit in this department being that of 

 Messrs. Fleuss, Dufl', k. Co. This apparatus is as useful 

 for searching expeditions in mines or other places filled 

 with noxious gases as it is for ordinary diving purposes. 

 No pipes are used in this system, but the diver, carrying 

 with him a small vessel holding a supply of oxygen gas 

 sufficient to last for four hours, breathes his own breath 

 over and o\-er again, the exhaled air being passed through a 

 filter containing caustic soda, wliich robs it of its poisonous 

 exhalations. 



