28 rbpout — 1859. 



ing match, regulated by a spring so as to give a cone of fire in the open air, in a 

 definite position with reference to the instrument, was exhibited. It is easily carried, 

 with or without the aid of a shoulder- strap, and can be used by the observer stand- 

 ing up, and simply holding the entire apparatus in his hands, without a stand or 

 rest of any kind. Its indications distinguish positive from negative, and are reducible 

 to absolute measure on the spot. The author gave the result of a determination 

 which he had made, with the assistance of Mr. Joule, on the Links, a piece of level 

 ground near the sea, beside the city of Aberdeen, about 8 a.m. on the preceding day 

 (September 14), under a cloudless sky, and with a light north-west wind blowing, 

 with the insulating stand of the collecting part of the apparatus buried in the 

 ground, and the electrometer removed to a distance of 5 or 6 yards and connected 

 by a fine wire with the collecting conductor. The height of the match was 3 feet 

 above the ground, and the observer at the electrometer lay on the ground to render 

 the electrical influence of his own body on the match insensible. The result showed 

 a difference of potentials between the earth (negative) and the air (positive) at the 

 match equal to that of 1 1 5 elements of Daniel's battery, and, therefore, at that time 

 and place, the aerial electromotive force per foot amounted to that of thirty-eight 

 Daniel's cells. 



On the Cause of Magnetism. By G. V. Towler. 



On Changes of Deviation of the Compass on Board Iron Ships by "heeling" 

 with Experiments on Board the ' City of Baltimore,' ' Aphrodite] ' Simla] 

 and * Slieve Donard.' By John T. Towson. 



The author explained the manner in which the Compass Committee was first 

 formed, in accordance with the advice of the Section, and stated that two reports 

 had been drawn up, which, with the advice of the Astronomer Royal, had been 

 printed and " presented to both Houses of Parliament by command of Her Ma- 

 jesty." He thanked the Astronomer Royal for his valuable advice and support. 

 There were matters of consideration which the Compass Committee deemed incom- 

 plete : the one was the change which took place in iron ships in proceeding to the 

 opposite hemisphere ; the other, the change that was produced by what is technically 

 denominated 'heeling,' thatis/when the deck of a vessel leaned over, through the 

 action of the wind or otherwise : if, when looking towards the bow, it slanted down- 

 wards to the right, it was said to heel starboard ; if to the left, to heel port. The first 

 question was undertaken by the late respected Rev. Dr. Scoresby, who proceeded to 

 Australia in the ' Royal Charter,' and whose exertions in the pursuit of this branch of 

 the inquiry shortened a most valuable life. The second question was the subject of 

 his present report. Having described the principles on which his graphic illustration 

 was constructed, the author pointed out the unexpected amount of deviation which 

 this source of disturbance (heeling) brought about, amounting in most instances, when 

 the ship's head was in the position to produce the maximum effect, to two or three 

 points in the standard compass, and to a greater amount so far as the steering com- 

 pass is concerned. He remarked on several particulars connected with this investi- 

 gation. Generally the north end of the compass was drawn to the upper side of the 

 ship — the case with seven out of nine compasses on board the ' City of Baltimore;' 

 but in the two steering compasses the needles were drawn in a contrary direction. 

 He explained the theory on which this disturbance arose, partly from subpolar mag- 

 netism below the compass, and partly from the disturbance of the inductive magnetism 

 of the ships. In such ships as those under consideration, the following empirical rule 

 held good with respect to compasses favourably placed. When the vertical force, as 

 determined either by vibration experiments or torsion on board the ship, maintained 

 the ratio, as compared with the vertical force on shore, of nine to fourteen, little or 

 no effect was produced by heeling in the same hemisphere and latitude. And in the 

 case of the 'Simla' this plan of predicting the amount of error was adopted: a 

 moveable upright magnet was applied so as to produce the before-named vertical 

 force, when it was found, "with magnet in," no error was produced, although " with 

 magnet out" it amounted to 21° from changing a heel of 10° starboard to 10° port. 

 There appeared to be another remarkable result. He believed that when a ship was 



