28 REPORT — 1841. 



which, with Mr. Dury,he had lately the honour of submitting to his Royal Highness 

 Prince Albert. The points treated of were — 



The defective condition of ordinary needles employed in sea-compasses, and the 

 method used by Dr. Scoresby to test their condition, by applying them to a highly- 

 magnetized hardened bar of the best cast steel. 



The nature of the needles which Dr. Scoresby recommends to be substituted for 

 the former. They are hardened throughout, and previous to being used, are tested 

 by being applied to the bar already mentioned. 



The application of delicate needles and large bar-magnets to measure the thickness 

 of rocks, &c., and other materials, in mines, railway tunnels, &c. 



The construction and method of magnetizing of a pair of bar-magnets, containing 

 192 thin steel plates fourteen inches long and one and a half inch broad, bound to- 

 gether with tape. They are very unusually powerful. 



On the Influence of Mountains on Temperature in the Winter in certain parts 

 of the Northern Hemisphere. By Thomas Hopkins. 



It was stated by Mr. Hopkins, that between the latitudes of 40° and 70° north, 

 there is in the same parallels a great difference of temperature, particularly in the 

 winter, amounting in some cases to as much as 40° or even 50° of Fahrenheit. The 

 western coasts of the two continents are much warmer than the eastern, and as 

 the winds generally blow from the sea to the western coasts, it has been inferred, 

 that the prevailing winds passing over sea to the western coasts, and over land to 

 the eastern, was the cause of the difference in the temperature. This inference is 

 not, however, in accordance with facts, as the low temperature is not proportioned 

 to the distance from the western coast. 



Hadley's theory represents the tropical atmosphere as rising and flowing over 

 at the top towards the polar regions, and returning when cooled, flowing along on 

 the surface of the earth. This inequality of temperature in the atmosphere would 

 cause an upper current to flow north, and an under current to flow south. But 

 the unequal velocities of the different parts of the earth's surface from the equator 

 to the pole modify the course of these currents, and make the upper a south-west 

 and the lower a north-east current, as shown by lines on a Mercator's chart. 



Tliis theory, true in its leading principles, does not account for what occurs on 

 the earth's surface, because it does not take in all the causes that are in operation, 

 which causes materially modify the general results. 



The Polar current, in flowing from the north-eastern part towards the south-west, 

 meets with elevations of the land, and is consequently, along a diagonal stripe in 

 the direction of the general currents, obstructed in its progress, and sometimes 

 stopped, and obliged to turn back as an upper current towards the pole ; while be- 

 yond the obstruction, nearer to the equator, the tropical or upper current not being 

 met by a polar current along this line, flows towards the obstruction, from whence 

 it returns, partially cooled, as an under current. 



In the New world, the ridge of mountains which extends from Mexico by the 

 Rocky Mountains to the Frozen Ocean, crosses the diagonal line of the great at- 

 mospherical currents, and constitutes such an obstruction as that described. 



In the Old world similar ridges extend from the southern point of the Himalaya 

 Mountains to the Swiss Alps, including the range of the Himalaya, Hindoo Koosh, 

 Central Asia, Armenia, Circassia, the Carpathian Mountains, and the Illyrian and 

 Swiss Alps, and the climates found to the north-east of these chains are materially 

 different from those which exist to the south-west. 



The greatest differences of climate in those parts are found in the beginning of win- 

 ter, and are, it is presumed, caused by the different quantities of atmospheric steam 

 condensed in the respective parts. 



Over the tropical seas a quantity of steam exists in the atmosphere sufficient to 

 give a dew-point of 80°, making the steam one forty-eighth part of the whole atmo- 

 sphere. This steam, which if all condensed into water, would give a depth of about 

 nine inches, is regularly carried in the autumn and the beginning of the winter, 

 when the northern hemisphere is cooled, from the tropical regions in a north-east 

 direction towards the polar regions, or towards some obstructing elevation of the 



