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2, Description of a Sliding Scale for Facilitating the Use of 

 the Moist-bulb Hygrometer. By James Dalmahoy, Esq. 



The instrument described in the paper is made of German silver, 

 and is about a foot in length, and j^(y of an inch in breadth ; along 

 the middle of it there is a groove for a slider. On the right edge 

 of the groove is engraved a scale of inches, and on the left the de- 

 grees of temperature from 0° to 85° Fahrenheit, each being placed 

 exactly opposite that point of the scale of inches which measures the 

 corresponding tension of vapour. On the left edge of the slider is 

 engraved a scale of equal parts, each ^^ of an inch ; on the right 

 edge, and having the same zero, is a vernier, applicable to the scale 

 of inches. The lines on these scales are ten times larger than those 

 which the symbols in the dew-point formula represent, but their nu- 

 merical designations are not changed. 



Tho instrument is to be used as follows : — Find on the slider the 

 number which expresses the difference between the indications of 

 the dry and moist bulb thermometers, and bring it opposite the num- 

 ber on the left scale, denoting the temperature of the moist-bulb; 

 then zero on the slider will indicate, on the left scale, the tempera- 

 ture of the dew-point ; and on the right scale, the corresponding 

 force of vapour. 



The paper concludes by shewing that the ordinary hygrometric 

 formula, which suggested the idea of the sliding scale, indicates also 

 a geometrical construction for finding the temperature and tension 

 of vapour at the dew-point, which, however, would not be practically 

 applied with convenience. 



3. Account of Experiments to Measure the Direct Force of 



the Waves of the Atlantic and German Oceans. By 

 Thomas Stevenson. Communicated by David Stevenson, 

 Esq. 



Tho author has attempted to supply a great desideratum in the 

 practice of marine engineering, by instituting a series of experimenta 

 to ascertain what force the waves exert against opposing barriers. 



For this purpose he suggests, in some peculiar situations, the use 

 of columns of water or of air, by which the force of each wave can 

 be ascertained ; in the one case by the rise of the water-column, or 

 in the other by a pressure-gauge, shewing the same result in atmo- 

 spheres by compression. But in all the observations as yet made 

 he has used an instrument which may be termed a " telf-r-'gistering 



