1903.] 



On Central American JtJarthquakes, etc. 



403 



picked up and recorded precisely as they are emitted, as has been 

 tested by intercalating a siphon recorder in a much diluted tapping 

 circuit at the sending end, so as to get a record with which to make 

 comparison. The traces obtained at the two ends are identical to a 

 surprising degree. 



The mercury level has an adjustment which is easily made. One 

 precaution is to keep the rim of the wheel clear of dust, which is done 

 by a cork or leather pad pressed lightly against it by a spring. 



The instrument is not at all sensitive to tremor, and requires no 

 particular delicacy of adjustment. The wheel has to be positive, the 

 mercury negative. 



A telephone in circuit, through a transformer or otherwise, affords 

 an easy method of discriminating the signals by ear. The speed of the 

 wheel gives another convenient adjustment to suit various circum- 

 stances. 



''On Central American Earthquakes, particularly the Earthquake 

 of 1838." By Admiral Sir John Dalrymple Hay, Bart., 

 G.C.B., F.K.S. Eeceived March 6 —Bead March 19, 1903. 



The very interesting report of Dr. Tempest Anderson and Dr. J. 

 S. Flett on "Recent Volcanic Eruptions in the West Indies," induces 

 me to suggest that inquiries should be made in Colombia and in 

 Central America as to disturbances in those regions, in order to trace 

 the connection existing between the earthquakes and volcanic erup- 

 tions which are there so prevalent, and those in the West Indies. 



Doubtless Mr. Welby, who has just returned to his post at Sta. Fe 

 de Bogota, might be able to obtain thence some information on this 

 matter. 



In the British Association Keport, of 1858, upon Earthquakes, those 

 of 1835 and of 1841 are given ; but, unfortunately, no information is 

 given as to the effect of those disturbances from any British source. 



The British Association in both cases seem to have been mainly 

 indebted for their information to the Academie, and hence the effects in 

 Martinique and Guadeloupe are quoted, but nothing is reported from 

 our West India Islands. 



One of the most terrible disturbances in its effects, that of 1838, is 

 not even alluded to. The only record of it is in the work of E. G. 

 Squier, late Charge d' Affaires from the U.S. of America to the Repub- 

 lics of Central America (2 vols., Appleton, New York, 1852), who 

 was commissioned by his Government to report upon that region in 

 reference to the Nicaraguan Canal. Vol. 1 has the map ; vol. 2, pp, 

 114, 115, and p. 162 alludes to the eruptions of Cosequina in 1838> 



