TRANSACTIONS OF THE SECTIONS. 



39 



convenient scale, the number of knots per hour the ship is going ; from this point 

 draw a pencil line parallel to the direction of the wind as observed by the aneino- 

 scope (i. e. the apparent direction to which the wind is going) ; set off on this hne 

 the number of knots per hour as shown by the anemometer ; draw a line from the 

 centre of the circle to this last point. The length of this line by the scale adopted 

 gives the tnie velocity of the wind, and its direction (carried backwards) shows the 

 point/row which the wind is coming. A parallel ruler divided on the edge is all 

 that is required besides the slate. It would be easy enough to contrive some 

 mechanism to save the trouble of drawing lin^s, but it would not, I believe, be any 

 real simplification, and would increase the expense. The train of indicating wheels 

 might be so arranged that they at once indicate knots per hour without reference 

 to tables, and can be readily set to zero for a fresh observation." 



On a remarkable Hail-Storm in North Staffordshire. With some Casts of the 

 Hailstones. By R. Garner. 

 This storm, which came from the N.W. in the afternoon of the 22nd of July last, 

 between four and five o'clock, continued with great violence for about half an hour, — 

 some of the masses of ice which fell being li inch in diameter, and of course doing 

 corresponding injury, for instance, breaking more than twenty large squares of glass 

 in the rather small house of his (the writers's) next-door neighbour, and those of 

 his own Wardian case. Most of the hailstones seemed to have nodulated nuclei, 

 containing numerous particles of air, and externally to these were formed irregular 

 conglomerations of ice, looking like a mass of imperfect but transparent crystals. 

 The storm was attended with gusts of wind and thunder, and was of a very limited 

 and defined extent ; but to the south of the writer's residence, about four miles 

 away, near the Barlaston Station, a violent wind fr6m an opposite direction, S.W. 

 or S.S.W., occurred at the same hour, without rain or hail, the ravages of which 

 could afterwards be traced for a length of two miles, with a breadth of only from 

 50 to 100 yards. Oaks were deprived by it of their largest limbs, poplars broken at 

 the height of 8 or 12 feet from the ground, and an alder, 50 feet high, was uprooted 

 and carried some distance. The clouds were extremely dark for a great extent of 

 country. An artist took some casts of such hailstones as he picked up, by no means 

 the largest. These the writer exhibited with a drawing. 



On Isothermal Lines. By Professor Hennessy, M.R.I. A. 

 After some preliminary remarks as to the general influence of the distribution of 

 land and water on the forms of isothermal lines, the author proceeded to discuss 

 the distribution of these lines in islands. By considering an island situated so as 

 to have its shores bathed by a warm oceanic current, if the influence of direct solar 

 radiation be obstructed, it appears that the isothermals would be closed curves 

 surrounding the centre of the island and having some relation to its coast line. The 

 influence of ranges of mountains, and in general of inequalities in the surface of the 

 island, as well as the modifying action of general winds, and the resulting changes 

 in the shapes of the isothermals, were explained. By the introduction of solar 

 radiation, it now follows from the mathematical theory of heat that the entire quan- 

 tity of heat received by a unit of surface of the island will depend on two principal 

 terms : one, a function of the distance of the point from the coast, and capable of 

 being expressed in some cases as a function of the difference of latitude of that point 

 and the nearest point on the coast ; and, secondly, of a term depending on the 

 latitude and on an elliptic function of the second order having for its modulus the 

 sine of the inclination of the equator to the ecliptic. It hence follows that the effect 

 of solar radiation will be to transport the centres of all the closed isothermals 

 towards the pole of the hemisphere in which the island is situated. Some of the 

 lines may thus ultimately terminate at the coast with their convex sides turned 

 towards the equator, while others may still continue as closed curves in the in- 

 terior. If the influence of difference of latitude and direct solar radiation were 

 greatly predominant compared to other causes affecting the temperature of the 

 island, the isothermals might all terminate on the coast. If the continents may 

 be considered as immense islands so circumstanced, they become subjects for the 



