Professor Trowbridge's Lecture.

A large audience gathered yesterday afternoon in the lecture-room of the Jefferson Physical Laboratory on the occasion of Professor J. Trowbridge's lecture on "The scientific appliances of the Jefferson Physical Laboratory and the scientific work now being done there."

The first part of the lecture was a detailed description of the laboratory. The laboratory, Prof. Trowbridge said, is divided into two equal parts, one for elementary work and the other for special research. The large lecture-room, intended for general elementary lectures, is fitted up with the best modern appliances, with running water, with high-pressure hot water, with electric currents, with oxygen-hydrogen lamps, etc. The room above is the elementary; etc. The room above is the elementary; it is sixty feet by sixty feet, the largest of its kind, and is used by one hundred and thirty students. The excellent work done in this laboratory is exerting a great influnce over the country, and preparatory schools, especially Exeter, are establishing physical laboratories on the same plan. The western part of the building is devoted to special work. Here everything depends on stability of position. Besides small recitation-rooms and small laboratories, there are small rooms where the professors, assistants and advanced students can work without any disturbance of their instruments. In the basement, and in the first story, stone tables, each supported by its own column of masonry, and without contact with the floors, furnish firm support for the instruments. In the centre of the western wing there is a large rectangular tower, standing on an independent foundation, and isolated from the surrounding rooms; this tower is designed for investigations demanding extraordinary stability or great height. To avoid the influence of magnetism as much as possible, all pipes and nails in the western wing are made of brass.

The machine-room in the basement of the east end is one of the most important resources of the laboratory. It is here that the professors and advanced students materialize their ideas, and make their new apparatus. The work now being done is manifold. Professor Hall is at present busy in investigating how much steam is lost in the cylinder of an engine when in work. On account of the extreme heat thermometers cannot be used, and Professor Hall is therefore employing a very delicate electrical instrument. The relation of light to electricity and magnetism is being worked up by Mr. D. W. Shea. The apparatus is arranged in such a manner as to investigate whether light is a manifestation of electricity or not. Professor B. O. Peirce and Dr. Wilson are trying to determine the rate of flow of electricity into large reservoirs, for instance, into cables; in this investigation the greatest accuracy is necessary, as extremely small fractional parts come into play. Professor J. Trowbridge and Dr. S. Sheldon are at work on Electro motive forces, while Professor J. Trowbridge and Mr. Sabine propose to study the surface to the moon and determine its character by means of the absorption of the ultra-violet rays by surfaces of rock, ice and snow.