560 Progress in Science. [Odtober, 



through the glass, then several sparks in air will occur before another spark 

 will traverse the glass block again. Curiously enough, the spark in glass, as 

 in air, seems to render its path a worse conductor than before, for it rarely 

 happens that two sparks in a thick block go even partially by the same route, 

 though the conducting points remain in exactly the same position. 



The apparatus employed to pierce glass blocks is constructed as follows : — 

 Two glass hollow columns, a and b (Fig. 23), are provided with five wires along 

 their wires, the space about the wires being filled in with a mixture of wax and 

 resin. These pillars are made very broad at one end, which is ground flat, 

 and are provided with brass caps and binding screws at the other. They are 

 cemented with wax and resin by the broad ends to the block of glass, c, to be 

 pierced, the frame shown in the cut greatly facilitating the process. 



Employed to illuminate a Gassiot's cascade when a secondary condenser of 

 eight coated panes is in circuit, and an interruption or spark in air likewise 

 interposed, the amount of luminosity is truly surprising, and greatly exceeds 

 anything that we have seen with any other coil, even those made by Mr. 

 Ritchie to give 15-inch sparks. 



When coupled for quantity, the spark length is reduced to 12 inches, and 

 the quantity is conspicuously increased, as is indicated by the sound and the 

 aureola. When the poles are about 4 inches apart, this aureola may be blown 

 into a flame-like surface, extending 3 inches from the line of discharge. Con- 

 nected with a battery of four Leyden jars, the sparks are deafening, and afford 

 light enough to illuminate a zeotrope disk 4 feet in diameter, so as to make 

 the movement of its figures perfectly distinct at a distance of 60 feet. It is of 

 interest to note in conclusion that a determination of the resistances made by 

 Professor Morton gave for the resistance of the primary wire 0*13 of a unit 

 (Brit. Ass.), and of the secondary wire 40,400 units. 



Remarkable Electro-Magnet. — With the intention of attempting in conjunction 

 with Professor Mayer to solve various outstanding problems in diamagnetism, 

 in which unsatisfactory or negative results only have been obtained hitherto, 

 Professor Morton has had made by Messrs. Wallace and Sons, of Ansonia, 

 Connecticut, an electro- magnet of unusual form and of very great size. The 

 poles of the core, which is made of the best wrought iron, are 3 feet 3 inches 

 in height and 6 inches in diameter. They are hollow, the diameter of the 

 bore being 3 \ inches, and the thickness of the cylinder is therefore but 

 x\ inches, which is a little greater than the thickness required for total electro- 

 magnetic effect, as determined by Professor Mayer in accordance with the 

 principles made known by him in a recent number of the " American Journal 

 of Science." The diameter of the wire is one-fifth of an inch, and its total 

 length is about 2000 feet. It is wound upon eight brass spools, which can be 

 taken off or set on the core at pleasure. The weight of the magnet when 

 complete is 1540 lbs. — that of each spool 112 lbs. It is proposed to employ 

 three such galvanic batteries as were described in connection with the induc- 

 tion coil to supply an adequate galvanic current, and to connect them for 

 quantity. This will give a total area of zinc surface amounting to 27 square 

 feet. As yet no experiments have been made with a view of testing the 

 performances of this mammoth magnet, but I hope shortly to present some 

 account of them to the readers of this journal. 



On the Projection of Magnetic Spectra, Cohesion Figures, &>c, upon the 

 Screen. — A very ingenious apparatus was recently exhibited before the Ame- 

 rican Institute by Professor Morton, for the projection upon a vertical screen 

 of the images of objects, such for example, as waves in a tank of water, 

 cohesion figures of various liquids, magnetic spectra, and the like, which can 

 only be produced satisfactorily when the objects are maintained in a perfectly 

 horizontal position. The original idea and general plan of the instrument 

 shown was, as the speaker stated, due to Professor J. P. Cooke, of Cambridge, 

 his own work in connection with it being confined to the devising of a 

 convenient mechanical arrangement of parts, the improvement of the combi- 

 nation of condensing lenses with the reflecting lenses so as to secure a white 

 and evenly illuminated field on the screen, and the discovery that an ordinary 



