VIII. EVAPOROMETERS. 713 



can be brought under similar conditions of temperature, &c., and the eva- 

 porations compared for any temperature. The apparatus was especially 

 designed to determine the proper amount of water which should be dis- 

 charged by the artificial drainage system of the Fen Land. 



2899. Integrator of Sun's Heat. 



Scottish Meteorological Society. 



When the water in the globe expands, some of it passes out at the bent 

 upper tube. The level of the water is kept constant by a supply from the 

 cistern which communicates with the globe by the india-rubber ball which acts 

 as a valve. 



Note. The instrument, which is in principle a weight thermometer, may 

 also be used for ascertaining the mean temperature of the air. Designed by 

 Thomas Stevenson, C.E., E.R.S.E., Honorary Secretary. 



2900. Instrument, designed to ascertain the temperatures at 

 which visible vapour is found. Scottish Meteorological Society. 



Water is heated in the main chamber by a lamp beneath, and its temper- 

 ature is read at the point when vapour appears on one of the pieces of glass 

 which are made to revolve slowly above the open end branch tube, and again 

 read as the water cools, at the instant when condensation ceases to be 

 observed. Designed by Thomas Stevenson, -C.E., F.R.S.E., Honorary 

 Secretary. 



2901. Ebermayer's Evaporation Apparatus, for deter- 

 mining the degree of evaporation of different kinds of soil. 



Prof. Ebermayer, Aschaffenburg. 



The evaporating apparatus and the earth thermometer are described at 

 greater extent in " Die physikalischen Einwirkungen des Waldes auf Luft 

 " und Boden," von E. Ebcrniayer, Aschaffenburg, 1873. 



2902. Merger* stern's Atmometer. W. Apel, Cottingen, 



Morgenstern's atmometer differs from every other by its being founded on 

 the principles of capillarity and of Mariotte's bottle. 



The evaporating vessel is filled with siliceous sand, below which there 

 may be placed a flat stone. This sand is saturated with water by capillarity; 

 any loss of water by evaporation is at once replaced by a corresponding 

 volume of water from a burette. This burette forms a Mariotte's bottle, 

 the upper part of which is closed against the outer air by means of mercury. 

 A tube, bent in the shape of a horseshoe, of which one branch enters the 

 burette from below, conducts air into the latter in proportion as water is lost 

 through evaporation. When a large portion of the burette has become filled 

 with air, the danger arises that the air column on expanding, by a possible 

 rise of temperature, would exert a pressure upon the water below it in the 

 burette, and thus lead to an over-saturation of the sand. To prevent this 

 the branch of the last-mentioned tube which is placed outside the basin is 

 provided with a small globular vessel, into which the water, pushed on by 

 the expansion of the air column, enters. With progressing evaporation 

 this water returns again into the -burette, or can later be drawn into the 

 burette. This globular vessel is further intended for the filling of the burette 

 with water, which purpose is accomplished by fixing to the open end an 

 india-rubber tube, dipping into water, and sucking at the upper end of the 

 burette. Before the burette is completely filled the india-rubber tube is 

 removed, and the sucking at the upper end of the burette resumed, until, in 



