246 



NATURE 



[July 12, 1894 



I am thankful to have had my attention called to the subject 

 by Mr. Reade just upon the eve of deoarture for a few weeks 

 among the glacier.^ of L'menak Bay, in Greenland. I will g've 

 special attention to the subject, and report upin mv return in 

 the autumn. G. Frederick Wright. 



Oberlin, Ohio, June 23. 



On a Recent Change in the Character of April. 



The months are all, of course, continually changing in tem- 

 perature, rainfall, &c. .\nd, as a rule, tho;e changes are not 

 long in one direction ; the curve of variation has many zig-zags. 

 Yei, by methods of averaging, one may sometimes detect a 

 gradual process of change extending through a good many 



1865 1868 1871 1874 1877 1880 1883 1886 1889 1892 



yean ; we might compare it 10 the slope of an ocean-swell 

 underlying the surface-ripples. The mean lemperalure of 

 April at Greenwich is a noteworthy example of this. 



Here are the values since 1865, and averaged in fives in a 

 second column :— 



Av. 



45 '4 

 455 

 45' 

 446 



452 

 46 S 

 47-8 



Thus from a maximum of 5o''2 in 1S67, the average went 

 down, with some slight interruption at one point, to 44 '6 in 

 18S9 {if. $6 degrees), the extreme actual values being 52° 9 

 in 1865 and 43''5 '" iSSS (difference 9'4 degrees^ Last year 

 and the present yield values in marked contrast to those just 

 before, and a pronounced rise appears in the average curve. 



The data for Paris and Geneva give results very similar, so 

 that the process is not merely local. Thus the smoothed values 

 for Geneva descend from 10 '6 C. in 1S64 to 7"9 in iSSq. 



A geneial, though less continuous, decline in the mean tem- 

 perature of the entire spring (March to May), at Greenwich, 

 may also be noticed. 



I do not know whether any cause can be assigned for pro- 

 longed changes like these in April : some of your readers may 

 be able to throw light on the matter. 



The accompanying diagram illustrates the change referred to. 



A. B. M. 



The Deposition of Ova by "Asterina Gibbosa." 



I RECENTLY brought back from Jersey three specimens of 

 Aslerina giblwsa, all of which deposited ova in the small aquaria 

 in which they were kept. As it appeared evident that the ova 

 exuded from the oral surface, two specimens were selected for 

 experiment. 



The first was placed with the oral surface uppermost in a 

 small gl.iss well, «ithjust sufficient water to cover it. When 

 examined about half an hour later, ova had exuded from a 

 genital poie on the oral surface, and had floated up to the top. 

 Had the opening been on the aboral surface, they would have 

 been retained beneath the starfish. 



The second specimen was then placed in a glass dish with the 

 aboral surface uppermost. Sufficient water was added to all'iw 

 the animal to be moved e.isily with a pair of forceps, but not 

 enough to enable the lube-feet to act. Consequently ova, if 

 deposited, could not float away. In this position it was left for 

 about an hour. When turneil, so as to tiring the oral surface 

 uppermost, it was seen that ova had exuded. The starfish was 

 killed with the eggs still adhering. 



The .sexes of starfish are generally said to be separate. Uut 

 in this case only three specimens were brought : all deposited 

 ova, and in one small aquarium there are now young Asterinas. 



HkNRV SCHtRRE.N. 



BIFILAR PENDULUM FOR MEASURING 

 EARTH-TILTS. 



INSTRUMENTS designed for measuring movements 

 of the earth's crust belong to two classes. The first 

 consists of seismographs which register the amplitude 

 and period of the rapid vibrations of earthquake-shocks, 

 and by their records enable the velocity and acceleration 

 of an earth-particle at any instant to be determined. The 

 second class includes nadiranes and various forms of 

 pendulums (such as the bifilar pendulum here described) 

 which are, or should be, unaffected by vibrations of short 

 period, and which indicate only slow lilts or bendings of 

 the ground, show'ng the change of inclination at any 

 spot, the r.ite at which it is taking pl.ice, and, if periodic, 

 the length of its period. No part of the earth, so far as 

 we know, is free from such movements. Every day, and 

 every year, the surface of the ground at any spot tilts 

 forward and backward through a small angle, perhaps 

 not exceeding a small fraction of a second. Sometimes 

 regular pulsations arc observed, each .1 very few seconds 

 or minutes in duration, and lasting, it may be, for hours ; 

 at other times the tilting is irregular and occasionally 

 abrupt ; but invariably it is so slight, and takes place so 

 slowly, that without the aid of refined instruments it could 

 never be perceived. 



The report of the Earth Tremor Committee (British 

 Assoc. Report, 1893, pp. 291-303), presented at the last 

 meeting of the IJritish Association, contains an account 

 of a new bifilar pendulum designed by Mr. Horace 

 Darwin, and of some of the first experiments made with 

 it at Birmingham. This preliminary trial brought to 

 light one or two slight defects which Mr. Darwin has 



