TRANSACTIONS OF THE SECTIONS. 61 



It is, however, very desirable that depths thus estimated should be tested by 

 attaching the instrument to soimding fines, and that any necessary corrections 

 should be made in the tables. 



Such a comparison and correction woidd render the indications of the gauge 

 valuable when strong cuiTents make the use of the lead uncertain. 



A correction is required for fi-iction, yet to be determined, and a correction for 

 the variation of volume with change of temperature, as shown in the preceding 

 Table, which is based upon very niunerous and accurate experiments. 



On a Daily Weather Map ; on Admiral FitzRoy's Paper presented to Section A. 

 relative to the Royal Charter Storm ; and on some Meteor oloyical Documents 

 relating to Mr. Green's Balloon Ascents. By J. Glaishee, F.R.S. 



On the Cloud Mirror and Sunshine Recorder. By J. T. Goddaed. 



The Cloud Mirror was simply a mirror of a circular form with the points of 

 the compass marked on its frame ; this being presented face upwards to the sky, 

 and having its centre con-ectly marked and placed horizontal with the north point 

 of instrument towards the south meridian, enabled a person to observe the direction 

 from which the clouds were moving. The Sunshine Recorder was a piece of pho- 

 tographic paper placed in the bottom of a box blackened inside, the top of which 

 had in the centre a small circular hole, through which a slender beam of sunlight 

 coidd be admitted to pass on to the photographic paper. When the sun did not 

 shine, no mark was left on the paper ; when it did, its varying diurnal course left a 

 corresponding line on the paper, its position marking the hours of sunshine, and 

 its breadth and depth of shade indicating the gi-eater or less radiating power of the 

 sun. By inserting a thick glass disc or plano-convex lens in the box, the number 

 of hours' registry would be made equal to a simimer day's sunshine. 



On the Connexion between Storms and Vertical Disturhayices of the Atmosphere. 



By Professor Hennesst, F.R.S. 

 _ As storms are usually preceded by the contact of masses of air of different den- 

 sities and different degrees of elasticity, it follows that anterior to such storms a 

 process of connexion may exist between the heterogeneous columns of the atmo- 

 sphere. Under such circimistances, the sudden indraught of smoke in chimneys 

 and the whirling about of light objects near the ground had frequently been noticed. 

 The author endeavoiu-ed to make more precise observations by the aid of a vane, 

 which shows the presence of upward and downward ciu-rents in the atmosphere, 

 while also indicating the horizontal direction of the wind. Diu-ing the winter of 

 1860-61, he found that most of the stomas were preceded by more or less violent 

 vertical movements of the atmosphere. Such movements were especially obser- 

 vable before the great gale of February 9*. The analogy between some of the 

 vertical motions observed in the vane and those of the water-barometer foimerly 

 erected by Professor Uaniell in the apartments of the Royal Society was pointed 

 out, and fi-esh residts were anticipated fi-om the renewed erection of this kind of 

 instrument by Mr. Glaisher. The general conclusion to which Professor Hennessy 

 has been led, is, that during the comparative absence of horizontal motion in the 

 air, energetic vertical cim-ents may be grouped among the most certain symptoms 

 of approaching disturbances on a gi'ander scale. 



On the Theories of Glacial Motion. By William Hopkins, M.A., LL.D. F.R.S. 

 The author firet gave distinct definitions of temis designating those properties of 

 bodies with which we are necessarily concerned in investigations connected with 

 glacial phenomena, such as solidity, viscosity, extensibility, elasticity, and the like. 

 According to those views, which rested on l)r. Tyndall's experiment of reo-elation 

 ice must uecessai-Uy be considered as solid. Proceeding on this hypothesis, Mr. Hop- 

 kins stated the pressures and tensions to which a glacial mass must be subjected at 

 any internal point. He showed how the internal tensions woidd exactly account for 

 the fonnation of open fissiu'es or crevasses, according to the law which they were 



* Proceedings of the Royal Irish Academy, vol. vii. p. 494. 



