17'-' 



UNDULATORY FORCES. ELECTRICITY. [THB HYDRO-M-BCI-MO JCACHIVB. 



Fig. 2, bo Uken M a pattern, and 

 which we gave the recipe, be used, any 



illustrated in 

 material of w 



may, at a trifling expense, put themaelvea in 

 pomieaion of one of these ingenious electrical con- 

 trivances. 



rm of gutta-percha machine was mventwl 

 one year ago-and was, we believe, exhibited at the 

 Exhiliitit.il in Hydo-jiark, in 1851. It consists of an 

 eodlen band of gutta-jiercha, running over two rollers. 



.bun are formed of hnrd hair-brushes ; and its 

 general construction U illustrated in tho following 



nstrumenta, as, in the absence of those of larger size, a 

 preat iiumU-r of the experiments wo shall mention in 

 >ur future page* ""y l>e tried. 



Another, and singular source of electricity, is that 

 from the friction of pure water; which U effected by 

 means of steam as it condenses at ita exit from the 

 Machines constructed for this purpose are 

 called hydro-floctrio machines. The largest of the kind 

 is that at the Polytechnic Institution, R*ge; 

 and as we there had it in daily use for several months 

 together, we shall be somewhat particular in describing 

 ita construction, and the effect* which nmy be obtained 

 from it. The following engraving illustrates the ex- 

 ternal appearance of this instrument 

 r*. 3. 



A trprwnt the bnd of (rnttt-peretia ; B B ire the two rnbbon ; C i 

 the hn.n<- which tunw ihe upper roller; the under one moving hy the 

 frtetlon of the (rutu-percha against iu surface; D U the conductor, 

 which extends IB two armi, ended with point* facing the gutta-percha 



As we have never tried this form of machine, we 

 can give no particulars with respect to its value. 

 It, however, has the advantages of ready construction. 

 alight cost, and, of course, does not require amalgama- 

 tion or extended preparation before use, beyond that of 

 cleaning all the surfaces from dust and dirt. 



Perhaps the simplest form of electrical machine is 

 that of tho electrophorus, which, at a most trifling ex- 

 penditure of trouble and expense, presents an oppor- 

 tunity for any one to try a vast number of electrical 

 experiments. It may be constructed as follows : 



Into a tray of sheet-tin or zinc, half an inch deep, and 

 twelve inches in diameter, pour melted yellow resin till 

 the liquid reaches the top. This forms the sole of the 

 electrophorus. A circular piece of zinc plate, nine inches 

 in diameter, should have fixed to its centre a gutta- 

 percha handle nine inches long. The plate should be 

 quite level, and its edges 

 smooth. The arrangement 

 is represented in the annexed 

 figure. 



The mode of exciting tho 

 electrophorus is very simple. 

 The resin is, of course, al- 

 lowed to cool, and it may 

 then be nibbed briskly, by 

 means of warm, dry flannel. 

 The metal plate, held by the 

 handle, is then placed on the 

 resin plate. The <o;i of the 

 zinc is then to be touched by 

 the finger, and it is then to 

 <-d a few inches. On 

 prenentini; tin- knuckle. 



fig. 



A represent* the reitn Mile ; 

 B the irutu-percha handle ; 

 C the line plat*. 



spark will pass to it. This process may be repeat- I for 

 a long time, as tho plate only requires occasional 

 rubbing by moans of tho flannel. A continual upply 

 of electricity may thus IM> obtained : tin- only i> 

 venicnco which is experienced, is that of continually 

 lifting the zinc plate to obtain the spark. 



We recommend our readers, cspe. -ially the i 

 portion of them, to make one of these useful 



A A represents the boiler, which is about eight feet 

 long, including the smoke-box. H B are six glass legs, 

 which support and insulate the boiler. C is a 001 fitted 

 with iron spikes or points. This box can be removed 

 nearer or further from tho boiler, and, by its proximity 

 thereto, influences the length and intensity of the spark. 

 D D are the handles, by means of which the steam is 

 permitted to pass into, or to be shut from, a series 

 tubes, which are curved into the form of the letter S, 

 and are represented at E E. These tubes are terminated 

 by circular knobs, which enclose jets of partridg' 

 shaped of a cylindrical form, and having a jet somewhat 

 resembling a bat's-wing gas-burner. As the steam 

 passes from the boiler through the series of bent tubes 

 to which we have alluded, it is partially condensed, and 

 arrives at the jets in the state of minute particles of 

 water. The pressure of the steam drives them with 

 great force against the side of the jet, and thus the 

 sides of the jet take the place of the rubber in this 

 machine, and the pure water that of the glass. Tho 

 action of tho hydro-electric is therefore analogous to 

 that of the glass machine in most respects. It lias 

 been stated, that the water used in the boiler should lie 

 almost, if not entirely, free from mineral substance. 

 Wo may, however, state, that having used this machine 

 for illustrating lectures on elect licity for a long time, 

 in daily succession, it was always supplied with water 

 abounding with lime and oxide of iron. Can-, how- 

 ever, was always taken to prevent " priming ;" and 

 the neglect of that may have eiveti rise to the opinion 

 in respect to the necessity of pure water, to wr ich we. 

 have referred. 



Tho effects produced by this machine vary with tho 

 pressure, all other circumstances being equal. We have 

 employed pressure varying from thirty pounds on tho 

 square inch to that of I'M : ami up to ninety pounds 

 the spark was in direct proportion to tho pressure. 

 Thus, if a spark of six inches was afforded by a pressure 

 of thirty pounds, one a i inches in length was 



produced by a pressure of ninety pounds : but beyond 



