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!■ buildings near the laboratory to inter- fere withtlieemploj'oientofeuDliglit for optical purposes from dawn to twilighi. The west- ern wing contains no iron, all the gaa-pipoB and steam-pipes being made of hraas. This wing has a separate entrance, and can be iso-

��yCE. [Toi- v.. No. in.

sight entirely within the building nearly two hundred feet long.

The portion between the two wings U Af voted to recitation-rooms and cabinets. lecUirc-room capable of seating an audience^ of three hundred is placed on the first floor of I

���lated from the eastern wing, which contains the large leclure-room and the clementarj' lalrora- tory. The vibrations resulting from the move- ment of classes are tima obviated in the west- ern portion. Each room in the basement and first floor of the western end ia provided with brick piere, which are so arranged that instru- ments placed upon the south-west or the north- west corner ptcra can command long lines of sight east and west, and north and south. In the centre of the western wing, below the floor of the basement, is a constant-temperature room. This room is at the base of a tower, the walls of which arc at least a foot from the main walls of the building. This tower rises to the roof, from which, however, it is entirely separate. In this way the effect of the wind ia prevented from communicating vibrations to this inner tower. In the tower are placed large shelves of slat«, which ser\-e as piere

��the eastern wing. Immediately over it is tlxt^ large elementary laboratory sixty by sixty feci. Connected with the latter are several rooms for special investigations, which do not require the great steadiness of the western end. Immedi- ately beneath the lecture-room is the workshop. together with a battery and a mercury-room. I'ower is conveyed to the workshop through a lar^e tunnel which connects with .in oatsiile cngine-liouse. in which is placeil a twcnty-flve horse [lower engine and a seven horse jtower gas-engine, together with two dynamo-electric engines.

The ground upon which the laboratory: placed consists of gravel, with a substratum a cla}', which, however, is below the lowest fouil^ dation of the laboratory. The nearest stre is more than three hundred feet distant, and fi is found that no prejudicial vibrations are com

��� ��on the second and third floors. The ari'ange- ment of rooms in the western wing is such that any room can be entered from the main hall without going through any other raom. Moreover, two or more rooms can be thrown together if any experiment demands such an arrangement There is gas and water in each room. Provision is also made for a line of

��municated to the piers. A vessel of met placed upon them, however, shows slight pations and vibrations. The shelves placed the isolated tower are steadier than the pien, This is probably due to the effect of the ou^ side walla of the building in cutting off the surface vibrations, and suggests, that, if thd future builders of physical laboratories de^i* ideal stendiness, Ihey should sink walla outflii

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