378 



was in advance of observation, at present observation is in advance 

 of theory ; which mathematicians are therefore called upon to re- 

 model and perfect. 



The author proceeds to consider the effect of the Moon's declina- 

 tion on the Tides at Liverpool; which, as before observed, it is ne- 

 cessary to eliminate, in order to obtain the Solar inequality ; and 

 gives an explanation of various formulae and tables constructed for 

 that object. He then investigates the laws of the solar inequalities, 

 first, as to the heights; and secondly, as to the times of high water at 

 Liverpool, by applying to them these methods of calculation. 



March 10, 1836. 



FRANCIS BAILY, Esq., Vice-President, and Treas., in the Chair. 



Edward John Johnson, Esq., Commander, R.N., was elected a 

 Fellow of the Society. 



" Report of Magnetic Experiments tried on board an Iron Steam- 

 Vessel, by order of the Right Hon. the Lords Commissioners of the 

 Admiralty." By Edward J. Johnson, Esq., Commander, R.N., ac- 

 companied by plans of the vessel, and tables showing the horizontal 

 deflection of the Magnetic Needle at different positions on board, to- 

 gether with the dip and magnetic intensity observed at those posi- 

 tions, and compared with that obtained on shore with the same in- 

 struments. Communicated by Captain Beaufort, R.N., F.R.S., 

 Hydrographer to the Admiralty; by command of the Right Hon. the 

 Lords Commissioners of the Admiralty. 



This report commences with a description of the iron steam-vessel, 

 the " Garryowen," belonging to the City of Dublin Steam Packet 

 Company, and built by the Messrs. Laird, of Liverpool. She is con- 

 structed of malleable iron, is 281 tons burthen, and draws only b\ 

 feet water, although the weight of iron in the hull, machinery, &c. 

 is 180 tons. 



This vessel was placed under the directions of the author, in Tar- 

 bert Bay, on the Shannon, on the 19th of October. 1835, for the pur- 

 pose of investigating its local attractions on the compass. The me- 

 thods which were adopted with that view are given ; together with 

 tables of the results of the several experiments, and plans of the va- 

 rious parts of the Garryowen. The horizontal deflections of the 

 magnetic needle at different situations in the vessel were observed, 

 for the purpose of ascertaining the most advantageous place for a 

 steering compass, and also for the application of Professor Barlow's 

 correcting plate : and the dip and intensity in these situations were, 

 at the same time, noted. 



An experiment is detailed, showing that where several magnetic 

 needles, freely suspended, were placed upon the quay, in Tarbert 

 Bay, and the vessel warped from the anchorage towards them, first 

 with her head in that direction and then with her stern, opposite de- 

 flections were produced : in the first case all the needles showing a 



