NATURE 



139 



THURSDAY, JUNE 25, 1874 



THE NEW PHYSICAL LABORATORY OF 

 THE UNIVERSITY OF CAMBRIDGE 



ON the i5th inst., at a congregation held in the Senate 

 House, Cambridge, the Cavendish Laboratory was 

 formally presented to the University by the Chancellor. 

 The genius for research possessed by Prof. Clerk Maxwell 

 and the fact that it is open to all students of the Univer- 

 sity of Cambridge for researches will, if we mistake not, 

 make this before long a building very noteworthy in 

 Kiiglish science. We therefore put before our readers, as 

 prominently as we can, a description of it. 



The Cavendish Laboratory has been erected entirely 

 at the expense of his Grace William Cavendish, Duke of 

 Devonshire, K.G., Chancellor of the University, who has 

 also signified his intention of supplying it with the 

 apparatus necessary for a complete physical laboratory. 

 The building consists principally of three floors, of which 

 the accompanying figures show the plan on a scale of 

 32 ft. to the inch ; Fig. i representing the ground-floor, 

 and Figs. 2 and 3 the first and second floors respec- 

 tively. The west front consists entirely of Ancaster stone ; 

 with the exception of the lecture-room and the staircase, 

 which will presently be described, the only ornate portion 

 of the building is the great gateway, X Fig. i, situated 

 near the south end of this front. The doors, which are 

 very massive, are beautifully carved in oak, and bear, in 

 old English letters, the inscription " IMagna opera Domini 

 cxquisita in omncs voluntates ejus," which is the Vulgate 

 version of Psalm cxi. 2. Over the gateway are the arms 

 of the Duke of Devonshire on the left, and the University 

 aims on the right, the motto of the Cavendish family, 

 " Cavendo tutus," occupying the centre ; and the whole is 

 surmounted with a beautifully carved statue of the Duke in 

 his robes as Chancellor of the University, and bearing 

 in his hand the Cavendish laboratory. The lower portion 

 of the building on the right of the entrance is occupied 

 by the resident attendant. The external walls are 2 ft. 

 thick, the foundation being at a depth of 15 ft. below the 

 surface : with the exception of the west front, the tower, 

 and the portion occupied by the lecture-room, they are 

 built of brick, with Ancaster stone dressings. The 

 tower (marked A in the plans), which is about 17 ft. 

 by 14 ft. 6 in. internal measurement, and 59 ft. in height, 

 contains a very handsome stone staircase with carved 

 oak balustrades. 



In describing the internal arrangements seriatim, we 

 shall commence with the room at the east end of the 

 ground-floor marked B in Fig. i. This room is set 

 apart for magnetic and other observations requiring 

 great steadiness. At a is a brick pier about 18 in. high, 

 with a stone top about 4 ft. square. This pier is quite 

 distinct from the tiled pavement of the room, the brick- 

 work being commenced at a depth of about 18 in. below 

 the pavement, and this resting on a foundation of concrete 

 about 18 in. thick. On this pedestal is placed the great 

 electro-dynamometer of the" British Association, the two 

 large coils of which are each about half a metre in dia- 

 meter, and each contains 225 turns of No. 20 copper wire. 

 The diameter of each circle of wire has been accurately 

 measured, as has also the distance betweeen the two 

 Vol. X. — No. 243 



bobbins, which is about equal to the radius of either. The 

 resistance of each coil has also been determined, and 

 thus all the electrical constants of this instrument are 

 known with great accuracy. It is by comparison with 

 these coils that the electrical constants of all the other 

 electro-magnetic apparatus in the laboratory will be 

 determined. For example, the magnitude and position of 

 each circle of wire in each coil being known, the coefficient 

 of induction of the first coil on the second can be at once 

 found. Suppose, then, we wish to find the coefficient of 

 induction of a third circuit upon a fourth whose resistance 

 is known. Let the same primary current be sent through 

 the first and third circuits, and let resistances be intro- 

 duced in the second or fourth until the currents in the 

 two latter are equal. Then the electromotive forces in the 

 second and fourth circuits are proportional to the whole 

 resistance in the circuits, and thus the coefficient of in- 

 duction of the two pairs of circuits are compared. 



At h and c are stone slabs each 4 ft. square, supported 

 on foundations similar to those last described. On the 

 slab at b is placed a unifilar magnetometer of the 

 pattern adopted at Kew. In the upper part of the 

 north wall of this room is a small window for the 

 purpose of determining the direction of the meridian by 

 astronomical observations. This direction being once 

 determined, vertical mirrors will be placed opposite each 

 other on the walls, each mirror being supported by three 

 screws and accurately adjusted by means of nuts so as to 

 serve the purpose of collimation marks. Three mirrors 

 will be placed respectively on the north, east, and south 

 walls of the room, but the fourth mirror will be fixed on 

 the west wall of the room marked F in Fig. i, in such a 

 position as to be visible through the doorways from the 

 mirror on the north wall of room B. The room marked 

 C in Fig. I is called the clock room. In it is a stone pier, 

 ii, on foundations separate from the rest of the building 

 and intended to carry the principal clock. This clock 

 will be in electric communication with the other clocks in 

 the building, and will from time to time be compared with 

 the clock at the Astronomical Observatory. In this room 

 is also erected a massive stone frame, c, intended to carry 

 an experimental pendulum. This, like the clock pedestal, 

 is erected on a foundation similar to that which supports 

 the electro-dynamometer. 



Each of the rooms B and C is about 30 ft. by 

 20 ft. The windows in all the rooms throughout the 

 building have wooden shutters fitted to them, by 

 which they can be completely darkened. On the in- 

 side of each window is a large stone shelf, and on 

 the outside a similar shelf in the same plane with it, so 

 that an instrument may be erected with some of its feet 

 inside and some outside the window, a small channel 

 being left between the two to allow the escape of rain- 

 water. The room marked E in Fig. i has two large 

 windows on the north side, and will be used exclusively for 

 balances. The best balance at present in the laboratory 

 was constructed by Oertling, and when loaded with a 

 kilogramme in each pan will turn to the weight of a milli- 

 gramme. This balance, while capable of carrying a very 

 considerable weight, is sufficiently delicate for most phy- 

 sical purposes. 



The room marked F in Fig. i is called the heat 

 room ; in it will be conducted experiments in calo- 



