SCIENTIFIC EXPERIMENTAL APPARATUS. 441 



22. Wiedemann galvanometer, with two sets of coils and two kinds of 

 needles. Eeadiug by mirror and scale. 



23. Galvanometer with large wire for experiments on the damping 

 effect of the coils on the needle, and for determining resistances in ab- 

 solute measure. Designed by Eowland and made by Schneider, instru- 

 ment maker at the university. 



24. Tangent galvanometer J wooden circle, with a variety of coils of known 

 constant. 



25. Mirror galvanometer. 



26. Rowland's ivooden circle, 84 centimetres diameter, carefully laid up 

 out of maple wood, and containing seA^eral grooves on the edge to coii- 

 tiiin single wires. It is used to surround a galvanometer, when, by aid 

 of the electro-dynamometer, the horizontal intensity can be measured 

 at any instant. 



27. EJectro-dynamometer of form given in Maxwell's Electricity, Vol. II, 

 p. 330. Outer circles about 27.5 centimetres diameter, with 240 windings 

 on each side. Constant, G-, of outer coils 78.371 on cm. gm. second sys- 

 tem. Inner coils about 5.5 centimetres diameter, with 03 coils in each. 

 Moment of inertia of suspended coil accurately known. Constant cal- 

 culated and also determined by comparison with a tangent galvanometer 

 made of the circle described above. Made (partly) by Gurley, of Troy, 

 and circles wound and measured by Eowland. 



28. Electro-dynamometer, Quhicke's form for weak currents. Made by 

 Edelmann, of Munich. 



29. Standards of resistance, mounted so that they can be i)laced in 

 water 1 and 10 ohms, by Elliott ; 10, 100, and 1,000 ohms, by Warden, 

 Muirhead & Clark, of London ; also mounted in another style — 1, 10, 

 and 100 Siemens, units, by Siemens & Halske, of Berlin. Also thre« 

 copies of coil whose absolute resistance was determined by Eowland as 

 34.719 earthquad. -^ sec. 



30. Ecsistance coils in boxes, 1 to 10,000, and 10,000 to 100,000 ohms, 

 by Elliott, and 1 to 10,000 Siemens' units by Edelmann. 



31. Rowland's resistance coinparator. — Ten coils, of 10 ohms each, ar- 

 ranged so that they can be joined in series or abreast, thus making 1, 

 10, and 100 ohms, besides intermediate ones. Made by Schneider and 

 adjusted by Eowland. 



32. Two bridges of Jenkins's form for the accurate comparison of equal 

 resistances, and also a Wheatstone bridge, having wire of platinum- 

 iridium alloy one metre long, by Elliott. 



33. Magneto-electric machine for 1,200 candles, by Siemens Brothers, 

 London, with engine to drive it, and both Siemens's and Foucault'slamxjs. 

 Also a battery of GO large bichromate cells- 



34. Ri'hml-orff coil, spark 15 or 20 centimetres, by Euhmkorflf, of Paris. 



35. Roipland''s earth inductor, with brass circle, 30 centimetres diameter, 

 wound and measured by Eowland. Made by Meyerstein, of Gottingen. 



