Instructions in the Use of Meteorological Instruments (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1888 edition. Excerpt: ...on some surface which is a less powerful radiator. Where no grass can be obtained the thermometer should be placed on a large black board laid upon the ground. Under any circumstances a board gives a better measure of terrestrial radiation than grass; a small groove may be cut in it to receive the bulb and prevent the thermometer from rolling. It is much to be desired that some convenient method should be devised by which correct and comparable observations of radiation may be secured. HYGROMETRY. General Description Op The Instrument. There are various kinds of hygrometers, the observations of the amount of moisture in the air being taken in a direct, as well as in an indirect, manner. The most important instruments for direct observations are Daniell's and Regnault's, both of which require the employment of eiher to lower artificially the temperature of the instrument. Direct Hygro-Daniell's Hygrometer consists of two bulbs connected meters. together by a tube. One bulb is of black glass, the other of clear glass and coated with muslin. The liquid within the bulbs is ether, which has been made to boil when the instrument was sealed, so that all air should be expelled. The instrument will then act in a similar way to Wollaston's Cryophorus, and if a difference of temperature be produced between the two bulbs all the liquid will be transferred from the warmer to the colder bulb. The mode of taking an observation is the following: --The whole of the ether is caused to enter the black bulb, and a little ether is dropped on the muslin covering of the clear bulb. The evaporation of this ether lowers the temperature of this clear bulb, and causes the ether in the black bulb to distil over into the clear one. This process has the effect of lowering the...