262 



NATURE 



\Jan. 31, 1878 



cules coming up to the heater in equal numbers and with equal 

 velocities from all directions in front, and by molecules receding 

 from the heater equally in all directions, although with augmented 

 velocities. Under these circumstances there would be no differ- 

 ence in the pressure on the front and back of the disc, except 

 during the very brief period of adjustment. 



By making this assumption Prof. Reynolds leaves the part of 

 Hamlet out of the play ; for Crookes's force arises out of the 

 very circumstance which has been omitted, viz., that the mole- 

 cules that come up to the heater or cooler, arrive in the form of a 

 rain which predominates in a definite direction, a direction which 

 is normal to the heater and cooler in the simple case of their 

 being paiallel. G, Johnstone Stoney 



A Double Rainbow 



On the 28th inst., at about 6.30 p.m. while myself and some 

 ten or twelve other gentlemen were playing cricket, we were 

 surprised to see what we all considered a most novel phenome- 

 non — a double rainbow. The sky was cloudy and the weather 

 was thundery. At the time referred to a shower of rain fell ; 

 the sun was about 10° above the horizon, shining out very bril- 

 liantly and reflecting upon the waters of St. Vincent's Gulf. 

 Great wonder was expressed at the strange appearance, and 

 much curiosity as to the cause. 



The appearance was as follows : — There were two distinct and 

 well-defined bows ; the feet were united, but the apices were a 

 considerable distance apart. 



I am of opinion that the lower bow was caused by the direct 

 light of the sun, while the light reflected from the sea produced 

 the upper one. Thomas Noy^ 



WUlunga, South Australia, November 30 



SCIENCE IN TRAINING COLLEGES 



'T*HE Science and Art Department has just issued a 

 -*■ circular having an important bearing on the teach- 

 ing of science is to take in our training colleges, and 

 therefore also in elementary schools. 



The Lords of the Committee of Council on Education 

 believe that the time has arrived when a special exami- 

 nation should be instituted at a period of the year better 

 adapted to the training colleges than May, and that the 

 nature of the examination and the payments made on the 

 results should be modified to suit the circumstances of 

 those colleges. They have therefore determined that in 

 future a special examination in science shall be held in 

 training colleges in December, immediately before the 

 ordinary Christmas examination. 



The examination will not be open to acting teachers. 

 It will be held in those subjects only for which a special 

 course of instruction is provided in the time-table of the 

 College, and will be conducted by one of her Majesty's 

 inspectors or by an officer of the Science and Art Depart- 

 ment. Special committees will no longer be required for 

 the training colleges ; such returns as are necessary will 

 be made by the principal. No student in a training col- 

 lege will be allowed to attend the May examinations of 

 the Science and Art Department, except in physical 

 geography in May, 1878. 



The examination will be confined to the following nine 

 subjects : — i. Mathematics. 2. Theoretical Mechanics. 

 3. Applied Mechanics. 4. Acoustics, Light, and Heat. 

 5. Magnetism and Electricity. 6. Inorganic Chemistry, 

 including Practical Chemistry. 7. Animal Physiology. 

 8. Elementary Botany. 9. Physiography. 



No student will be permitted to take up more than two 

 subjects in any one year, and women will not be per- 

 mitted to take more than one subject in a year. 



The examination, except for mathematics, will be based 

 on the syllabus of the several subjects given in the Science 

 Directory ; but the two stages, elementary and advanced, 

 will be treated as a whole — one paper only being set. 

 These examination papers will be framed much as the 

 present May papers are framed, that is to say, with a 



certain number of compulsory questions and a certain 

 number of optional questions, some of the latter being 

 more difficult and more highly marked than the rest. 

 Questions will also be set on the method of teaching, 

 various branches of the subject. 



The successful students will be placed in the first or 

 second class, the standard for a second class being as 

 high as that of a good second class in the present advanced 

 stage, and for the first class of a ^ood first class in the 

 advanced stage. All students who pass will be registered 

 as qualified to earn payments on results and will receive 

 certificates, but no prizes will be given. A payment of 

 3/. will be made on account of each first class, and i/. los. 

 on account of each second class obtained by a student in 

 a training college. 



In addition to the payments for theoretical chemistry, 

 payments will be made for practical chemistry, of the 

 same amounts and on the same conditions as those 

 detailed in the Science Directory, § XLV. The circular 

 contains an appendix with a syllabus of the subjects for 

 mathematics in training colleges. We should advise all 

 interested in this matter to obtain a copy of the circular. 



SUN-SPOTS AND TERRESTRIAL MAGNETISM 



T HAVE seen only to-day the number of Nature (vol. 

 •*■ xvii. p. 220) containing a letter from Prof. Piazzi 

 Smyth on the above subject. I have also just now seen 

 for the first time a communication from M. Faye to the 

 French Academy of Sciences on July 30 last, in which 

 there is a reference to the same subject ; this I regret 

 much, as M. Faye, through an incomplete acquaintance 

 with my investigations, has drawn conclusions from one 

 of them which are not exact. I shall at present refer 

 only to the subject of Prof. Smyth's letter. 



M. Faye considers the difference of the periods found 

 by Dr. Lamont and myself for the diurnal oscillations of 

 the magnetic needle ( I o'4S years) and by Dr. Wolf from 

 the sun-spots (irii years), a sufficient proof that these 

 cycles are not synchronous, and therefore that there is no 

 causal connection between the two phenomena. Prof. 

 Smyth asks an explanation relatively to this difference, 

 upon the supposition that the two periods found are the 

 true mean durations of the cycles for the respective phe- 

 nomena. This supposition, however, is erroneous, and 

 consequently M. Faye's deductions from it fail. 



I have shown in a paper cited by M. Faye ' that if we 

 determine the epoch of the maximum diurnal oscillation 

 of the needle from Cassini's observations made at Paris, 

 and from Gilpin's observations made at London, we find 

 it to have occurred in 1787*25. This epoch agrees very 

 nearly with that deduced by Dr. Wolf for the maximum of 

 sun-spots. If we compare this epoch with that of the 

 last maximum which occurred for both phenomena near the 

 end of 1870, we shall obtain a mean duration of io"45 

 years, upon the assumption that eight cycles happened 

 between these two epochs. There is no difference 

 between Dr. Wolf and the magneticians excepting upon 

 the question whether there were eight or only seven 

 cycles. Dr. Lamont considers that the data existing 

 between 1787 and 1818 are worthless for a decision upon 

 this point, and by induction from the known cycles has 

 concluded that three cycles must have occurred in the 

 thirty-one years 1787 to 18 18. Dr. Wolf believes there 

 were only two. I have given the evidence which makes 

 the existence of three extremely probable. This question 

 has no relation whatever to the synchronism of the two 

 phenomena. 



If we could accept Dr. Wolf's view we should find, 

 as I have shown, that the mean duration of a cycle for 

 ^(?//z phenomena since 1787 would be ii'94 years, while 

 the sun-spot results for eight cycles determined by Dr. 



' "On the Decennial Period," Edinb, Trans , vol. xxvii. 



