METEOEOLOQICAL OBSERVATIONS. 237 



quantity of Potassium Iodide has been added. The Ozone 

 hberates the Iodine from the Potassium Iodide, and being in the 

 presence of starch the paper becomes blue. There are, however, 

 other substances often present in the atmosphere which produce 

 the same effect. The estimation is therefore not rehable. It is 

 not now included by the Royal Meteorological Society in their 

 scheme of observations. 



Wind. The direction of the wind has been determined by 

 vanes and its force estimated on a scale from to 6, from calm to 

 violent storm. The latter, though somewhat inaccurate, is the 

 method adopted at a large number of stations and, with experience, 

 yields useful results. For the accurate measurement of the 

 velocity with which wind travels a form of Anemometer (Greek 

 anemos, wind ; metron, a measure), known as Dr. Robinson's 

 Anemometer, is used at a number of stations. This instrument 

 consists essentially of four hemispherical cups, carried by four 

 arms attached to a vertical shaft, which is caused to rotate by the 

 action of the wind. The cups travel at a rate equal to one third 

 that of the wind, and the rotary motion is conveyed by a brass 

 rod to a drum driven by a clock, on which is placed a prepared 

 paper, and on which the wind velocity in miles per hour is 

 automatically traced. On examination of the tables it will be 

 seen that the prevailing winds are from the north-west and 

 south-west. 



In addition to the foregoing, observations are made on such 

 phenomena as Thunderstorms, Lunar and Solar Halos, Fogs, 

 etc., but space will not permit of their being dealt with in the 

 accompanying summaries. 



At various stations in Cornwall observations have been 

 made during the last century and half. The MS of the late 

 Dr. Borlase, of Ludgvan, deals with the period from 1754 to 

 1772. At Trewarthenick observations were made by Mr. Grregor 

 from 1765 to 1782. Notes now in the possession of this 

 Institution were made by Mr. James, at Redruth, from 1787 to 

 18('6; and the registers kept at Penzance by Mr. E. C. Giddy 

 from 1807 to 1827, are closely followed by Mr. Moyle's, at 

 Helston, continuous subsequently with our own. 



