NATURE 



{May g, 1872 



There are large gas holders, each holding eighteen 

 cubic feet of gas, in the laboratory. The construction of 

 the gas-holders is the same in principle as that used in 

 ordinary gas works. Each is, in fact, a large copper bell, 

 with its mouth dipped under water in a deep tank. All 

 the stop-cocks connected with the gas-holders are kept 

 constantly enclosed in vessels full of water, in order to 

 prevent leakage. The holders are filled at the beginning 

 of the session, one with oxygen and the other with hy- 

 drogen, and the lime light is thus always ready. 



With this brief account of the general arrangement of 

 the premises, I shall now describe more particularly some 

 of the apparatus and conveniences of the lecture-room 

 and laboratory, and some of the experimental investiga- 

 tions going on at present. 



The lecture-table in the lecture-room is 26ft. long- 

 by 2jft. It is not str.iight, but made of three 

 pieces, so as to be concave on the lecturer's side. A 

 portion of the top of the table is removable ; and when 

 it is taken away a large trough suited for showing waves 

 in water, and for other hydrodynamic experiments, is 

 exhibited. The trough is as long as the table, and is 

 i4in. broad and I2in. deep. It opens out at one end 



into a tank 26in. broad and 2oin. deep. The lecture- 

 table is, of course, furnished with the usual supply 

 of coal, gas, and water ; and besides pipes, which give 

 hot water and steam, are led to it. These pipes come 

 from the boilers that heat the air with which the Uni- 

 versity buildings are warmed and ventilated. Pipes are 

 also led to the table from the oxygen and hydrogen gas 

 holders in the lower laboratory, so that the oxyhydrogen 

 light is always at command at a moment's notice ; and it 

 is found a great convenience to have it so. It is used 

 very frequently, and enables iis to show to a lai'ge class 

 many experiments which we could not attempt with- 

 out it — experiments, for instance, with the reflecting gal- 

 vanometer and electrometer. The preparation for such ex- 

 periments generally requires much time and trouble ; but 

 with the permanent gas-holders filled once for all at the 

 beginning of the session and always ready, the oxyhydro- 

 gen light gives less trouble than an ordinary oil lamp. 



A powerful battery, which 1 shall have to describe im- 

 mediately, is always ready. Very thick electrodes, con- 

 sisting of nine ply of No. 16 copper wire of high con- 

 ducti\ity, plaited together, pass from binding screws on 

 the keture-tablc to the battery below the lecture-room 

 seats, and thence down to the lower laboratory. 



For instruments that require a very steady support 

 there are two pillars, one at each end of the lecture- 

 room tabic. These arc unconnected with the flooring. 



They pass through it without touching the boards, and 

 rest on the stone arches that cover a gateway beneath. 



On each side of the lecture-room there is a clock. One 

 of them is governed by electricity on Jones's principle ; 

 the other is an electric clock by Bain, and has a current 

 from a single cell for its motive. The former is an ordinary 

 eight-day clock, and is regulated in the following way : — 

 The bob of the pendulum is a hollow coil of insulated 

 wire. The plane of the coil is perpendicular to that of 

 the motion of the pendulum. The ends of the coil are 

 carried up the pendulum rod, and are connected with tele- 

 graph wires which proceed from the Observatory of Glas- 

 gow University. Fig. 2 gives a front view of the pen- 

 "dum, and shows the coil and a pair of permanent magnets 

 pointing towards the coil. When the pendulum swings 

 the hollow coil passes over the end of the magnet at each 

 side. Fig. 3 shows the suspension of the pendulum, 

 which consists of two flat springs, to which the wires 

 coming up the pendulum rod are joined. The springs 

 are attached to insulated brass pieces, to which are con- 

 nected, by means of binding screws, the wires from the 

 Observatory. There is a clock in the Observatory which is 

 constantly kept right, and by means of a make-and -break 

 arrangement connected with its pendulum, a galvanic cur- 



rent is sent once in each second through the wire that 

 proceeds from the Observatory, and thus through the coil 

 at the extremity of the pendulum of the clock that is to 

 be controlled. The coil is thus once in each second con- 

 \erted into a temporary magnet, and is attracted and re- 

 pelled by the permanent magnets between which it swings. 

 It will be readily understood that with this arrangement 

 a clock that is going slightly too slow m.ay be accelerated 

 a little, and a clock that is going slightly too fast may be 

 retarded a little, at each passage of the current. To be 

 able to set the controlled clock to agree with the Oljser- 

 vatory clock, it is necessary to have some way of dis- 

 tinguishing one second from another. This is done by 

 means of a galvanoscope or indicator, which is included 

 in the circuit, and which beats seconds with the currents. 

 The instrument is placed close to the clock in a place 

 convenient for comparison of it and the seconds liand of 

 the clock, It is arranged that there shall be no beat on 

 the last second of each minute ; and that in the last 

 minute of each hour there shall be an interval of twenty 

 seconds without any current. Thus the ends of the 

 minutes and the ends of the hours are distinguished. 



Of mechanical apparatus almost daily employed for 

 lecture illustrations may be mentioned various kinds of 

 vibrators, weighted spiral springs, a Coulomb's torsion 

 vibrator, a C)cloidal and a common pendulum arranged 

 for comparison, a friction brake, Sec, &c. Over the lee- 



