208 RLPOUT— 1880. 



drawing three oblique time lines at 9 a.m., 8 p.m., and 2 a.m. tln-ough the 

 St. Petersburg, Kew, and Vienna curves. There is more difficulty in 

 determining tlie exact instant at which any small disturbance occurs from 

 the Lisbon photographs, as the curves are not divided into hourly or two- 

 hourly divisions as at the other observatories. 



From 7.20 to 7.30 p.m. there is a sudden and large increase in the 

 horizontal force, which continues high until 7.40, and then suddenly 

 diminishes until nearly 8 p.m. 



On March 28, at 4.30 p.m., a slight eastward distui-bance takes place 

 at St. Petersburg, which is scarcel}^ perceived elsewhere. From 10.20 to 

 10.30 at all the stations the declination needle is moving westward, and 

 both the horizontal and vertical forces at Kew are increasing. From 

 10.30 to 10.40 the St. Petersburg needle continues to move west\vai-d, 

 and the horizontal and vertical forces continue to increase, but the Kew 

 needle moves back to the eastward fron 10.30 p.m. until 11.5 p.m., and 

 then westward to 11.30 p.m. From 10.20 p.m. to 1.25 a.m. on the 29th, 

 during which time there are two large distiarbances, there is a very close 

 resemblance between the St. Petersburg declination curve and the Kew 

 horizontal force curve, the disturbances being simultaneous, and a westerly 

 deflection at St. Petersburg corresponding to an increase of the horizontal 

 force at Kew. Taking the mean line of no disturbance as common to the 

 two, the hei<'-ht or depth of the Kew horizontal force curve is about one- 

 third of the height or depth of the St. Petersburg declination curve at 

 the same point. 



Plate IX. gives the St. Petersburg, Kew, and Vienna declination 

 curves and the horizontal and vertical force at Kew from 10 p.m. to 

 4 a.m. on March 28-29. 



The Vienna curve is very nearly the mean between the St. Petersburg- 

 and Kew declination curves between 10.30 and 11.30 p.m., but agrees abso- 

 lutely with the Kew curve for the part of the disturbance after midnight. 

 This disturbance was only slightly felt at Lisbon or at Coimbra. 

 According to the Stonyhursb record, the horizontal force magnet was 

 rather disturbed during the.'^e declination disturbances. 



On the next day (March 29), at 8.20 p.m., an e:isterly excursion begins, 

 which is identical at all stations until 8.45 p.m. ; but at this point the 

 St. Petersburg needle turns sharply back to the Avest, while the Kew and 

 Stonyhurst needles continue moving to the east, giving the greatest eastern 

 deflection for the month (15' 49")- This point is reached at 8.55 p.m., 

 whilst the corresponding western deflection at St. Petersburg is reached 

 about 9.5 p.m. The St" Petersburg curve then falls again, reaching its 

 lowest point at 9.30 p.m., after which the curves show a westward motion 

 of the needles at all stations. 



In Plate VIII., fig. 2, the time lines are drawn obliquely, as in the 

 curve for March 23-24. 



The Vienna curve is almost exactly the mean of the other two curves, 

 and the Lisbon and Coioibra curves very closely resemble the Vienna 

 curve for this disturbance. 



About 10.40 and again at 11.15 p.m. the St. Petersburg needle is de- 

 flected to the west, and the Kew needle toward the cast. The St. Peters- 

 burg needle reaches its maximum at 11.30 p.m., then both needles move 

 eastiwai-d until 12.10 a.m., after which the Kew needle begins to move 

 westward. At 12.30 a.m. the St. Petersburg needle also begins to 

 move westward, the curves very closely agree, and the disturbance is 

 veiy nearly over. 



