ON MAGNETIC OBSERVATIONS. 151 



was supplied by Mr. Whipple at the request of the Committee. It was 

 resolved to ask the First Lord of the Admiralty to consider a statement 

 of these requirements and to receive a deputation of the Committee and 

 other scientific men interested in the progress of terrestrial magnetism to 

 urge the establishment of a Magnetic Observatory at the Cape of Good 

 Hope, to be placed under the direction of Mr. Gill, the Director of the 

 Cape Royal Astronomical Observatory. In answer to Sir William 

 Thomson's application to the first Lord of the Admiralty, asking him to 

 receive a deputation on the subject, the First Lord requested that before 

 receiving a deputation he might have a statement of the requirements 

 with regard to the proposed magnetic observatory at the Cape to be asked 

 for by the deputation. 



At the request of Sir William Thomson a statement was laid by the 

 Chairman of the Committee before the first Lord of the Admiralty, 

 pointing out the importance of establishing a magnetic observatory at the 

 Cape of Good Hope and submitting a rough estimate of the cost of 

 observatory and apparatus and the necessary requirements. 



In a circular issued by the International Meteorological Committee, 

 which will meet in Munich in September next, the following questions 

 bearing on terrestrial magnetism are proposed for consideration : — 



Question 8.— Is it not necessary in the introduction to the publication of mag- 

 netic observations to give the absolute values of the normal readings of diti'erential 

 instruments ? 



Question 31. — Would it not be useful to come to an agreement as to the values 

 of the coordinates of magnetic curves registered by magnetographs ? 



To these questions, according to the opinion of this Committee, as 

 expressed in their reports, especially in their third report (1887), there 

 can be but one answer. The absolute values of the normal readings of 

 all magnetic instruments and their scale-values should be given in the 

 publication of magnetic records, and it would be convenient that the same 

 scale-values should be adopted at all Observatories for similar instruments. 

 The value recommended by this Committee for changes of horizontal and 

 vertical force is '0005 c.g.s. units for 1 centimetre of the scale. 



The Committee recommend that for self-registering magnetographs 

 the scale values for declination, horizontal force, and vertical force should 

 be arranged so that equal changes of ordinate correspond to equal in- 

 crements of absolute force in three directions at right angles to one 

 another, Sx, 8i/, and Sz being the changes in the horizontal force iii the 

 magnetic meridian, the horizontal force perpendicular to the magnetic 

 meridian and the vertical force respectively. 



The Committee also recommend that as far as possible the same time- 

 scale should be adopted for the registering magnetographs at different 

 Observatories, and that this scale should be 15 millimetres to the hour. 



Professor Lemstrom, of Helsingfors, also suggests the following ques- 

 tions for consideration : — 



Question 29. — What loethod should be employed for the study of earth-currents ? 



Question 30. — What is the extent of our knowledge of atmospheric electricity, 

 and how should we measure it quantitatively so as to get better results ' 



Question 32. — What instrument is best for studying the variations of vertical 

 intensity of terrestrial magnetism ? 



With regard to Question 32 the Committee are of opinion that Lloyd's 

 vertical-force magnetometer is a very satisfactory instrument for studying 

 the changes in the vertical magnetic force. 



