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 of expansion. Dalencé praised the skill of Sieur Hubin, glass-blower, whose address was Rue St. Martin, Paris, and says his success is due to the fact that "he knows the reasons for that which he does."

The sections in Dalencé's work on the barometer and hygrometer are interesting from the historical point of view, but do not fall within the province of these chapters.

Dalencé seldom gives credit to individuals for their shares in the development of the instruments he describes, and it is difficult to determine how many of the improvements mentioned by him were original with him, probably but few.

Mention may be here made of a complicated thermometer constructed by the expert Parisian glass-blower Hubin, although it was not described in print until 1725 (Reyher, Pneumatica). Two bulbed tubes were united at a reservoir, and bent in the shape of an U; both tubes were closed so that the apparatus was independent of air-pressure. The shorter arm of the U was filled with mercury up to the centre of the reservoir, the longer arm half filled with water, the remaining half, including the large bulb, containing air. When the