14 



NA TURE 



IMay 3, 1877 



action of radiation on the concave side, and that the 

 double speed with which the fly moves when no screen is 

 interposed is the sum of the attractive and repulsive 



actions. 1 1 ■ • 



14. Rai/ioinfler.—A two-disc, cup-shaped, aluminium 

 radiometer, lamp-blacked on the concave surfaces. In 

 this instrument the usual action of light is reversed, 

 rotation taking place, the bright convex side bemg re- 

 pelled, and the black concave attracted. When the light 

 shines only on the bright convex side, no movement is 

 produced, but when it shines on the black concave side, 

 this is attracted, producing rotation. 



i^.—J^ac/ioiiu'tcr.—A cup-shaped radiometer similar to 

 the above, but having the convex surfaces black and the 

 concave bright. Light shining on this instrument causes 

 it to rotate rapidly, the convex black being repelled. No 

 movement is produced on letting the light shine on the 

 bright concave surface, but good rotation is produced 

 when only the black convex surface is illuminated. 



16. A'(!(;'/t>/«t-A-r.— A multiple-disc, cup-shaped, turbine 

 radiometer, bright on both sides, working by the action 

 of warm water below and the coohng etfect of the air 

 above. 



17. Radiometer.— h four-armed metallic radiometer 

 with deep cups, bright on both sides. 



1 8. Radiomctcr.^K four-armed radiometer, the vanes 

 consisting of mica cups, bright on both sides. 



19. /v'fr^rwwt'/tv.— A four-armed radiometer having clear 

 mica vanes. The direction of motion being determined 

 by the angle formed by the mica vanes with the inner 

 surface of the glass bulb. 



DROUGHTS AND FAMINES IN SOUTHERN 

 INDIA ' 



THE paper on this subject, noted below, a copy of which we 

 have just received, will no doubt awaken much interest, 

 not only on account of its scientific bearings but also from its 

 bearings on so very practical a subject as the famines of India. 

 It is most gratifying to see that the subject has been taken up by 

 one who gives evidence on every page of rare capacity as a scien- 

 tific statistician. There is throughout an absence of straining 

 the facts before him beyond what tliey may leguimately bear, 

 and a skill in combining them so as to eliminate, as far as pos- 

 sible, what is merely accidental from the results ultimately 

 arrived at in their relation to the sun-spot period. 



The data discussed in Dr. Hunter's paper are the amounts of 

 the annual rainfall at Madras from 181310 1876, and the relative 

 number of sun-spots from 1810 to 1S76. The results of the 

 inquiry are given in the following six propositions : — 



1. That no uniform numerical relation can be detected between 

 the relative number of the sun-spots and the actual amount of 

 rainfall. 



2. That although no uniform numerical relation can be detected 

 between the relative number of sun-spots and the actual amount 

 of rainfall, yet that the minimum period in tlie cycle of sun-spols 

 is a period of regularly recurring and strongly marked drought in 

 Southern India. 



3. That, apart from any solar theory, an exammation of the 

 rain registers shows that a period of deficient rainfall recurs in 

 cycles of eleven years at Madras ; that this period consists of the 

 eleventh and second series of years in the cycle ; which two 

 series also contain six out of the seven years of minimum sun- 

 spots falling in this century up to 1878. 



4. That alter the period of minimum rainfall in the elevenlh 

 and second series of years in the cycle, the rainfall rises to a 

 maximum in the filth year ; afier which it .tgain declines to Us 

 minimum period in the eleventii and second years. 



5. That, apart from any solar theory, the statistical evidence 

 shows that the cycle of rainfall at M.adras has a marked coinci- 

 dence with a corresponding cycle of sun-spots ; that in this c)cle 

 of eleven years both the sun-spots and the rainfall reach their 

 minimum in the group consisting of the eleventh, first, and second 

 years ; that both tlie rainfall and the sun-spots then increase till 

 they both reach their maximum in the fifth year, after which they 



' "The Cycle of Drought .ird Famine in Southern India," by W. W. 

 Hunter, LL.D., Director-General of Statistics to the Government of India. 



decline together till both again enter their minimum period in 

 the eleventh, first, and scc.uid series of years. 



6. That while the statistical evidence discloses a cycle of 

 drought in .Southern India, coincident in a marked manner with 

 a corresponding cycle of sun-spots, it also tends to show that the 

 average rainfall of the years of minimum rainfall m the said 

 cycle appro.aches perilously near to the point of deficiency which 

 causes famine. That the average is, however, above that point ; 

 and that, while we have reason to apprehend recurring droughts 

 and frequent famines in these cyclic years of minimum rainfall, 

 the evidence is insufficient to warrant the prediction of a regularly 

 recurring famine. 



It will be observed that these results are strongly confirmatory 

 of the general conclusions arrived at by Meldrum and others, 

 who have examined the question from data collected from a large 

 area, and embracing an extended series of years, the only note- 

 worthy point of difference being the larger rainfall of the first 

 year of the c)cle, as compared with the eleventh and second 

 years which immediately precede and follow it. It is perhaps 

 only to be looked for that such an anomaly should be met with 

 in dealing with the rainfall of only one place, embracing a period 

 of sixty-lour years, seeing that the accidental occurrence of one 

 or two cyclones, accompanied with unusually heavy local rain- 

 fall, would be sufficient to produce the anomaly in question. 

 The anomaly would in all likelihood have disappeared if the area 

 of observation had been wider or the time of observation longer. 

 It is scarcely necessary to do more than point out the absolute 

 necessity of establishing physical observatories in order to obtain 

 the data for the investigation of the connection between the state 

 of the sun's surface and the state of terrestrial convection currents, 

 it being only through their cosmical relations that we may rea- 

 sonably hope to solve many of the more difficult problems of 

 meteorology, some of which lead to intensely practical issues. 



OUR ASTRONOMICAL COLUMN 



Mr. Gill's E.xpedition to Ascension.— In an address 

 to the Royal Astronomical Society on Apiil 8, 1S57, "On the 

 means which will be available for correcting the measure of the 

 sun's distance during the next twenty-five years," the Astro- 

 nomer-Royal directed attention to a method of making observa- 

 tions for parallax, not applicable to the planet Venus, but appli- 

 cable to Mars, namely, by " observing the displacement of Mars 

 in right ascension when he is far east of the meridian, and far 

 west of the meridian, as seen at a single observatory," and he 

 particularised the advantage of this method, and expressed his 

 opinion that it is " the best of all." The observations are not 

 attended with the very great expense which is involved in the 

 efficient observation of a transit of Venus, indeed if made at an 

 established observatory need entail little or no cost ; they may 

 be conducted by a single observer or series of observers, in the 

 latter case with a due regard to personal equation, and each 

 observatory co-operating in the work, will furnish a result quite 

 independent of the rest, so that the observer has the satisfaction 

 of knowing that by the method recommended his own observa- 

 tions alone will give a value for the most important unit of 

 measure in astronomy. The Astronomer-Royal confined his 

 remarks to the observation of differences of right ascension, 

 recommending as of the first consequence a firmly-mounted 

 equatorial, and as advantageous though not absolutely necessary 

 the chronographic method of transits first introduced by the 

 American astronomers. The oppositions of Mars in 1S60 and 

 1S62 were referred to with regard to their relative advantages for 

 such observations. 



Mr. Gill has taken a further and an important step in the 

 direction of utilising observations of Mars for the determination 

 of the solar parallax. Encouraged by Lord Lindsay's liberal 

 oR'er of the loan of the heliometer employed in the e.xpedition to 

 the Mauritius for the observation of the transit of Venus, Mr. Gill 

 proposes to leave England this month for the island of Ascension, 

 and to apply the heliometric method of measurement of distances 

 instead of observing differences of right ascension, as sug- 

 gested in the Astronomer-Royal's address, and as was stated 



