Sept. iT, 1874] 



NATURE 



411 



and as much geometry as is equivalent to the first book of 

 Euclid. They believe that it will be found sufficient to im- 

 part such further geometrical knowledge as may be required, 

 such, for instance, as a knowledge of the properties of similar 

 triangles — in the first instance, during the course of instruction in 

 mechanics. 



In reference to the order in which the other departments of 

 physics should be studied, the Committee do not think it pos- 

 sible to prescribe any one order that is necessarily preferable to 

 others that might be adopted; but they consider it desirable that 

 priority should be given to those branches in which the ideas 

 encountered at the outset of the study are most easily appre- 

 hended, and illustrations of which arc most frequently met with 

 in common experience. On these grounds they suggest that the 

 elementary parts of the science of heat may advantageously 

 folknv mechanics ; that elementary optics (including the laws of 

 reflexion and refraction, the formation of images, colour, chro- 

 matic dispersion, and the construction of the simple optical 

 instruments) should come next, and afterwards the elements of 

 electricity and magnetism.* When it is found possible to include 

 in the work of a school a fuller or more advanced course of 

 physics than that here indicated, the committee are of opinion 

 that the discretion of the master, guided by the circumstances of 

 ll'.c case, will best decide in what direction the extension shall 

 take place ; they suggest, however, that an early place in the 

 course should be given to elementary astronomy, both because it 

 furnishes tlie grandest and most perfect examples of the appli- 

 cation of dynamical principles, and because it promotes an 

 intelligent interest in plienomena which, in the most superficial 

 asi)ects at least, cannot fail to arrest the attention and familiarise 

 the mind with the wide range of application of physical laws. 



Tne connnittee arc strongly of opinion that no very l^eneficial 

 results can be looked for from the general introduction of physics 

 into school teaching, unless those who undertake to teach it have 

 themselves made it the subject of serious and continued study and 

 have also given special attention to the best methods of imparting 

 instinction in it. They therefore suggest that with a view to afford- 

 ing facilities to persons desirous of becoming teachers of physics 

 for familiarising themselves with the most efficient methods and 

 gaining experience in them, the Council of the British Asso- 

 ciation should invite the leading teachers of physics in the uni- 

 versities, colleges, and schools of the United Kingdom, to allow 

 such persons, under suitable regulation, to be present at the in- 

 structions given by them, and, when practicable, to act as tem- 

 porary assistants. The committee do not hereby mean that 

 aspirants to the teaching function should be encouraged to drop 

 in at random to hear any lecture by any established teacher who 

 happened to be within reach ; the kind of attendance they have 

 in view would be systematic and continued for not less than some 

 moderate period of time, such perhaps as two or three months, 

 agreed upon at starting. 



They believe that the benefits which might result from the 

 adoption of such a plan are very great ; the advantages to those 

 who might avail themselves of it are obvious, and while teachers 

 of eatablishfd success would have a chance of spreading widely 

 their methods of instruction, and in fact of founding schools of 

 discipline, the stimulus to exertion afforded by the consciousness 

 that they were being watched by men who were preparing them- 

 gelv,es to occupy positions similar to their own would be of the 

 Ijjpst gfTicient kind. 



SECTIONAL PROCEEDINGS 

 SECTION A— Mathem.\tics 

 On the appUialion of Kirchhoff's Rtiles for EUdru Circuils lo 

 the solution of a GcomUrkal PioMem, by Trof. Clerk-Maxwell, 



The "eometrical problem is as follows :— Let it be required to 

 arranged system of points so that the straight lines joining them 

 into rows and columns shall form a network such tliat the sum 

 of the squares of all these joining lines shall be a muumum, the 

 'first and last points of tlie first and last row being any four 

 •points given in space. The network may be regarded as a kmd 

 lof extensible surface, each thread of which has a tension m each 

 ■ segment proportioned to the length of the segment. The problem 

 is thus expressed as a statical problem, but the direct solution 

 would involve the consideration of a large number of unknown 

 quantities. 



• It sliould be slated tli.at one member of the committee did not appioye 

 of the order of the subjects suggested in the text. 



This number may be greatly reduced by means of the analogy 

 between this problem and the electrical problem of determining 

 the currents and potentials in the case of a network of wire 

 having square meshes, one corner of which is kept at a unit 

 potential, while that of the other three corners is zero. This 

 problem having been solved by Kirchhoff's method, the position 

 of any point P in the geometrical problem with reference to the 

 given points A B C D, is by finding the values ot the potentials 

 P,i Pb Pc Va of ''^s corresponding point in the electric problem 

 when the corners abed respectively are those of unit potential. 

 The position of P is then found by supposing p^ p,, p^ pj placed 

 at A 13 CD respectively, and determining P as the centre of gravity 

 of the four masses. 



Oil the Apparent Connection l>et;iiecii Sun-spot and Atmospheric 

 O:.oiie, byT. Moffat, M.D., F.G.S., &c. 



At the last meeting of the British Association, Mr. Smith, of 

 Birmingham, gave me a record of the number of new groups of 

 sun-spots which appeared in each year for a number of years, 

 and he asked me to compare the mean daily quantity of ozone 

 in each year with the number of groups. I have done so, and in 

 the following table I have given the mean daily quantity of ozone 

 for nineteen years (1851-1869) with the number of groups. 



It would appear from these figures that the maximum of sun- 

 spot gives a maximum of ozone, and that the minimum of sun-spct 

 gives the minimum of ozone. The years 1S54 and 1S63 appear 

 to be exceptional. In 1S54, however, ozone observations at 

 Ilawarden were suspended tor three months, which may account 

 for the iriegularity in that year. There is, I think, in these 

 results, sufficient to induce others to observe. 



On the employment of Charts on Gnonionic Projection for the 

 general purposes of Navigation, by G. J. Morrison. 



The object of this paper is to recommend the adoption for the 

 general purposes of navigation of charts on gnomonic projection, 

 instead of on Mercator's projection, for the loUowIng reasons : — 



1. The great circle course or shortest distance between any 

 two points on the earth's surface is shown by a straight line on 

 the chart. By means of a ruler, therefore, it is easy to find out 

 in one moment the position of the great circle track along the 

 whole course from point to point, and thus to see at a glance if 

 thcie be any obstacles in the way, whereas the plotting of a great 

 circle track on a Mercator chart involves the expenditure of a 

 great deal of time and trouble. 



2. When it is impossible to adopt the great circle course on 

 account of obstacles in the way, it is easy, in a few moments, to 

 lay down the best practicable cuuise, whereas it is very difficult 

 to do so on a Mercator chart. 



