42 REPORT — 1841. 



so much increase the friction on the agate planes, as to render the application of 

 the process in this part of the needle objectionable. 



The needles presented are of clock spring, and were magnetized in the ordinary 

 way, by double touch, previously to being subjected to the electro-metallic process. 

 Their weights before they had received the coating of gold were 225*4 grains and 

 222*1 grains, and afterwards 227'8 grains and 223'8 respectively; so that the coat- 

 ing of gold on the one is 2*4 grains, and on the other 1'7 grain. Previously to 

 the application of this process of gilding, it is quite necessary that the surface of the 

 needle should be well polished, and perfectly clean. Professor Christie remarked, 

 that in the specimens before the Section, which were first attempts, in consequence 

 of defect in the polish, the process had failed in particular points. This arose from his 

 desire that the original surface of these particular needles should not be much 

 rubbed down ; but the defect is one which with due care and attention may easily be 

 avoided. These needles still retained a considerable degree of magnetism, but this 

 was greatly increased on their being re-magnetized by means of two bar magnets, 

 then on the table. 



On the Use of the Sliding Rule, with an account of some New Lines pro- 

 posed for it. By J. Bateman. 



This communication, which was illustrated by a sliding-rule with a radius of 

 eight feet, the largest size yet graduated, embraced notices of the ordinary lines on a 

 sliding-rule ; the application of these to cask-gauging, by the use of a mean diameter, 

 calculated or obtained by peculiar graduations on the rule ; the proposal of Dr. 

 Young and others, to obtain the contents of casks by one setting of the rule, with- 

 out the previous finding of a mean ; the causes why these attempts have been un- 

 successful ; and a description of the line of special gauge points, lately invented by 

 Mr. WooUgar of Lewes (which required a double setting of the rule). The author 

 stated, that all that is wanted by the practical cask-gauger is the completion of Dr. 

 Young's lines, applied to casks of a spheroidal form, i. e. a graduation for finding the 

 contents of such casks at one setting of the rule. 



On Determining Distances hy the Telescope. By Edmund Bowman. 



Instead of a graduated scale in the common focus of the eye-glass and object-glass, 

 and a fixed measure held at an unknown (but limited) distance, the author advo- 

 cates the employment of a fixed interval in the common focus of the eye-glass and 

 object-glass, and a graduated staff held at the point whose distance is required to be 

 known. This method he fully developes and describes, and by a very simple pro- 

 cess makes the requisite correction for the varying distances from the object-glass 

 of images which are derived from unequal distances from the observer. The author 

 is of opinion, that, with suitable instruments and with adequate attention, observa- 

 tions may be made which shall give the distances truly to the one-thousandth part. 



On recent Discoveries in Voltaic Combination. By Mr. De Moleyns. 



On an Instrument for Drawing Circles in Perspective. By Mr, Grellet. 



Notice of certain Barometers invented by Mr. Bursill. By W. G. Gutch. 



(The instruments are patented.) 



Communications which arrived after the meeting broke up, were forwarded by 

 Sir David Brewster, "On Crystalline Reflexion;" by Dr. R. Deakin, "Registers of 

 Meteorological Instruments at the Baths of Lucca, in the Summer of 1840 ;" by 

 John Marshall, Esq., "Notice of the Fall of Rain in Low and High Ground near 

 Hallsteads, in Cumberland." 



