28 



NATURE 



[Afaj 9, 1872 



called the marine branch of hydrodynamics are of such 

 great value, has stated that ''he has never noticed a wave so 

 much as loft. high in loft. water, nor so much as 20ft. 

 high in 20ft. water, nor 30ft. high in five fathoms water ; 

 but he has seen waves approach very nearly to those limits." 

 Mr. Russell has not stated whether the depths of water 

 referred to aic ihose below the trough of the sea or below 

 the slill-watcr level. In my book on " Harbours" I gave 

 three observations on short waves from 2ft. 6in. to 3ft. 

 high, which corroborated Mr. Russell's statement, sup- 

 posing him to refer to the depth below the hollow. But 

 since that time I had an opportunity, during a N.E. swell 

 in July 1S70, of observing the depths in which waves of a 

 larger class broke at the Promenade Tier at Scarborough, 

 where the heights could be mearurcd with very consider- 

 able accuracy on the iron piles and open sloping slip or 

 grating at the seawaid end of the pier ; and the following 

 are the results ; — 



Heights of waves from hollow to crest. 



5 6 

 5 ° 

 5 o 



Li' 



5 3 = mean height. 



The mean depth of water below the trough was 

 loft. 3in. 



Heights of the highest waves from hollow to crest. 



6 o 

 6 o 

 8 o 

 6 o 

 6 o 



6 6 = mean height of highest waves. 



The mean depth of water below the trough was 

 13ft. 8oin. So that in both cases those waves did not 

 follow Mr. Russell's law. but irah' 7viu'ii tJic depths bcloiu 

 their troughs livre about tiuice their own height. 



It must not bo supposed, as is generally believed, that 

 the height of the crest above the mean level of the sea is 

 equal to the depression of the trough below that level ; for 

 Prof. Rankine has lately shown that this is not the case. 

 When /. = length of wave, H = height from trough to 

 crest. 



Crest above still water =— +7854-^. 



Trough below still water = - 



7S54 77- 



These formula?, he states, are exact only for water of 

 considerable depth as compared with the wave's length. 

 Edinburgh Thomas Stevenson 



CYCLONES IN THE INDIAN OCEAN 



OEVERAL cyclones have passed Mauritius since the 

 ^ latter part of January. From the 24th to the 30th 

 of that month the barometer at the Observatory fell from 

 29'888 to 29 70S inches, wiih the wind squally from E. 

 At 10 A.M. on the 30th it was intimated to the newspapers 

 that there were "indications of a hurricane approaching 

 the island ;" but at 2 P.M., the wind having in the interval 

 veered to N. of E , it was announced that there was 

 '•little danger." 



This storm was encountered by the schooner Emiiv, 

 on her passage from Tamatave, Irom Jan. 29 to Feb. i. 

 At the commencement of the gale, she was in 19" 31' S., 

 and 53° 30' v.. The wind veered from N.E. to E., S.E., 

 S., S.VV., W., and N.W., with a "tremendous sea and 



torrents of rain," and the lowest reading of the barometer 

 on board was 29^00 inches. The vessel escaped with the 

 loss of only a few sails. 



The storm then curved to the S. and E , and was expe- 

 rienced by the barques Cladiateur and Alibotsford on 

 Feb. 2 and 3, in 31'^ to 29° S., and 54° to 55° E. With 

 the former vessel the wind veered from E. to N.E. and N., 

 blowing at one time with great violence. The barometer 

 at 8 A.M. on the 2nd was at 28'8o, and the wind from 

 E.N.E. The Abbots/ard had the wind from the same 

 direction, and her barometer was at 28^40 at 5 A.M. on 

 the 2nd. Both vessels had a "tremendous sea and 

 ton cuts of rain," and they lost sails and bulwarks. 



On Feb. 5 the barometer at Mauritius, after rising to 

 29'79o, again began to fall, and on the 7th was at 29'6o6; 

 The wind was squally from S.E., and it veered to S. by 

 W., from which point there was a gentle breeze at 9.30 

 P.M. on the 7th, with fine clear weather. 



At 10 A.M. on the 7th it was announced that " the 

 weather of the last two or three days indicated the passage 

 of another storm, which then broke between E.N.E. and 

 E. ;" and at 10 A.M. on the following day that " the storm 

 had curved to the S. and S.E." 



This storm was encountered by the barc[ue Elisabeth, 

 from Melbourne to Mauritius, on the 7th and 8th. in 

 20° 16' S., and 68° E. The wind was strongest from 

 IC.N.E. to N.N.E., and the lowest barometer was 29'30. 

 There were " torrents of rain." By standing back to the 

 E. the Elizabetli avoided all danger. 



On Sunday, Feb. 11, the barometer at the Observa- 

 tory, after rising to 29870, again began to fall, with the 

 wind squally from S.E., and the weather fine. During 

 the 1 2th it fell 'oCo inch, and '090 inch more during the 

 13th, wilh the wind still squallj- from the same quarter. 

 At 10 A.M. on the 14th the following notice was sent to 

 the newspapers : — "A hurricane since the nth. It now 

 bears about E.N.E. of us. There are some signs that it 

 will pass to the E. and S. of the island, but there is 

 danger." The barometer still falling, and the wind in- 

 creasing to strong breezes from S. by E. to SS.E, at 

 3 P.M. a telegram was sent to Port Louis (6 miles ofif), 

 stating that "the centre of the hurricane was about 350 

 miles to the E.N.E., and approaching the island," and 

 soon afterwards storm signals were hoisted at the railway 

 stations. The barometer at 3 P.M. stood at 29612, and 

 the wind, which was then .S. by E , was blowing with an 

 estimated force of 2'5lbs. on the square foot. 



At 9 A.nr. on the 15th the barometer was at 29 '478, with 

 a strong gale from S.E., and it was estimated and an- 

 nounced that the " centre of the storm bore about N.N.E. 

 1 50 to 200 miles, and that it was still approaching the 

 island." At 3 P.M. the wind being from I'^S.E. to E. by 

 S. in increasing gales, and the barometer at 29382, it was 

 telegraphed to Port Louis that "the centre was about 150 

 miles to N. by E., and that it would probably pass, wilh 

 an increase of wind, to N.W. and W. of the island. With- 

 out doing much damage." 



During the night the wind increased considerably from 

 I'l.S.E. to E. by S., and the barometer attained its lowest 

 reading (29'328) at I A.M. on the 16th ; but the mercury 

 was oscillating, being at 2 .\,M. at 29"356, and at 3 a.m. 

 -9'33o ; ^nd the time of the greatest depression of the 

 mercury, as shown by the barograph (at the Magnetic 

 Observatory, three miles off) was 2.40 A..M. At 9 a.m. the 

 barometer was at 29^440, with the wind at E. to E. by N., 

 and it was announced that " the centre bore N.N.W., and 

 that there w.is no danger." 



The barometer then continued to rise, until, .at noon on 

 the iSth, it was at 29'i.82, with a moderate breeze from 

 N.E. 



It is woithy of remark that the wind never went beyond 

 N.N.E., but gradually backed to East. 



This storm was more or less encountered at sea by the 

 llarpesia, Gryfe, Oleander, St, (.',ertuai)ie, Misser, S. S. 



