44 



NATURE 



\_May 13, 1880 



metallic resistance of the circuit. Through the point B, thus 

 obtained, draw a tangent to the curve, touching it at c, and 

 cutting o A in D. Then the speed of the machine, corresponding 

 to the particular curve employed, must be diminished in the ratio 



5_5 in order that an exceedingly small arc may be just possible. 

 O A 



Tiie curve may also be employed to put into a somewhat dif- 

 ferent form the explanation given by Dr. Siemens at the Royal 

 Society respecting the occasional instability of the electric light 

 as produced by ordinary dynam-o-electric machines. The opera- 

 tion of all ordinary regulators is to part the carbons when the 

 current is greater than a certain amount, and to close them when 

 it is less ; initially the carbons are in contact. Through the 

 origin O, Fig. 6, draw the straight line O A, inclined at the angle 



representing the resistances of the circuit other than the arc, and 

 meeting the curve at A. The abscissa of the point A represents 

 the current which will pass if the lamp be prevented from ope- 

 rating. Let o N represent the current to which the lamp is 

 adju>ted ; then if the abscissa of A be greater than o N, the 

 carbons will part. Through N draw the ordinate B N, meeting 

 the curve in the point b; and parallel to OA draw a tangent 

 E D, touching the curve at D. If the point B is to the right of 

 D, or farther from the origin, the arc will persist ; but if B is to 

 the left of D, or nearer to the origin, the carbons will go on 

 parting, till the current suddenly fails and the light goes out. 

 If B, although to the right of D, is very near to it, a very small 

 reduction in the speed of the machine will suffice to extinguish 

 the light. Dr. Siemens gives greater stability to the light by 

 exciting the electromagnets of the machine by a shunt circuit, 

 instead of by the whole current. 



The success of burning more than one regulating lamp in 

 series depends on the use in the regulator of an electro-magnet, 

 excited by a high-resistance wire connecting the two opposed 

 carbons. The force of this magnet will depend upon the dif- 

 ference of potential in the arc, instead of depending, as in the 

 ordinary lamp, upon the current passing. Such a shunt magnet 

 has been employed in a variety of ways. The author has 

 arranged it as an attachment to an ordinary regulator ; the shunt 

 magnet actuates a key, which short-circuits the magnet of the 

 lamp when the carbons are too far parted, and so causes them 

 to clo^-e. 



In c inclusion the author ventures to remind engineers of the 

 following rule for determining the efficiency of any system of 

 electric lighting in which the electric arc is used, the arc being 

 neither exceptionally long nor exceptionally short. Measure the 

 difference of potential of the arc, and also the current passing 

 through it, in volts and webers respectively ; then the product of 

 these quantities, divided by 746, is the horse-power developed 

 in that arc. It is then known that the difference between the 

 horse-power developed in the arc and the horse-power expended 

 to drive the machine must be absolutely wasted, and has been 

 expended in heating either the iron of the machine or the copper 

 conducting wires. 



PRELIMINARY REPORT B V TIIE COMMITTEE 

 ON SOLAR PHYSICS APPOINTED BY THE 

 LORDS OF THE COMMITTEE OF COUNCIL 

 ON EDUCATION 



" CIR, — In reply to Mr. MacLeod's letter of November 20, 



""^ 1879, calling upon us, pending the preparation of our 



General Report, to give a brief summary of the progress already 



made, and to state at the same time what work was in hand, and 



such other facts as we might think it desirable to mention, to 

 enable their Lordships to determine whether they shall apply to 

 the Lords Commissioners of Her Majesty's Treasury for an 

 extension of the vote for another year, we have the honour now 

 to submit the following report. 



" The Committee have had thirteen formal meetings. la 

 addition to this several members of the Committee have carried 

 out special branches of the inquiry ; and Mr. Lockyer, as 

 arranged when the Committee was appointed, has been charged 

 with the general conduct of the observational and experimental 

 work at South Kensington. The Committee consider that Mr. 

 Lockyer by his laboratory work and comparison of the results 

 w-ith solar phenomena, has brought together a great body of 

 evidence tending prima facie to conclusions of the utmost 

 importance. The labour and difficulty of the research are, 

 however, so great that much additional time and attention must 

 continue to be bestowed on it before the questions thus raised 

 can be considered as finally settled ; and the Committee think it 

 of much importance that the researches now being carried on 

 should not be interrupted. 



" The Committee have been in correspondence w ith the Indian 

 Government, the Astronomer-Royal, the Directors of the Ob- 

 servatories at Wilna, Melbourne, Mauritius, Kew, Moscow, 

 Toronto, Paris, Lalermo, Princeton, and with Dr. Warren De 

 la Rue. From all of these promises of valuable co-operation 

 and assistance have been received. To the Astronomer-Royal 

 our thanks are specially due for the manner in which he has met 

 us in the matter, placing all the information bearing on the sub- 

 ject in the Royal Observatory at our service. 



" A few months before the appointment of the Committee, daily 

 photographs of the sun had been commenced by order of the 

 Government of India under the Surveyor-General at Dehra, 

 N.W. Provinces, the photographs being transmitted to Mr. 

 Lockyer for reduction. 



" LTnfortunately the observer, Mr. Meins, late of the R.E., sent 

 from this count'-y, after having been trained at Chatham and 

 South Kensington, died suddenly in the early part of the year, 

 and the continuity of the daily record was thus broken. In 

 August the Government of India requested to be informed as to 

 the importance of the continuance of the records thus interrupted, 

 and the following letter was sent in reply : — 



"' Science and Art Department, London, S.W., 

 "'z-jth November, 1879 



" ' Sir,— In reply to your letter dated August 10, 1S79, inviting 

 remarks relative to the importance of continuing certain solar 

 observations which were recently instituted in India, and sug- 

 gestions as to future arrangements if it should be decided that 

 the observations are to be continued for an indefinite period, I 

 beg leave to submit to you, for the information of Lord Cran- 

 brook, the following explanation : — 



" 'In their General Report the Science Commissioners recom- 

 mended the establishment of a system of physical (as distinguished 

 from astronomical) observations on the sun, and pointed out the 

 advantages which Northern India offers for this study. A 

 memorial w-as more recently presented to Government, signed by 

 a number of our leading scientific men, urging the carrying out 

 of this recommendation. 



" ' In compliance with these recommendations the British 

 Government as a preliminary step appointed a Committee on 

 Solar Physics, whose duty it should be to make trial of methods 

 of observation, collect observed re.-ults, &c., and who were 

 specially charged with the reduction of such observations as 

 should be made in India. As a consequence of this arrangement 

 the Government of India authorised the employment of the late 

 Mr. Meins for the purpose of taking photographs of the sun in 

 India, and a series of such photographs was prepared by him 

 and has been sent home to be dealt with. The following brief 

 statement w ill show how superior the climate of India is to our 

 own for observations of this kind. The Astronomer-Roy.al has 

 been so kind as to furnish the Committee with a list of the solar 

 photographs taken at the Royal Observatory during the period 

 2ist luly, 1S73, to iSth July, 1S79, over a part of which Mr, 

 Meins' work extended. It should be mentioned that in both 

 places alike the rule was to take three photographs daily, in the 

 morning, about noon, in the afternoon, when clear views of the 

 sun could be obtained. In the rare cases in which a fourth 

 photograph was taken in the same day in India, it is not 

 included in the following list : — 



