July 30, 1903] 



NA TURE 



309 



irefrangible end of the spectrum, acting in this respect 

 an a manner analogous to the hydrogen lines. It is found 

 that the potassium curve is exactly similar to the hydrogen, 

 having a horizontal asymptote which corresponds to the 

 -limit of the series. Not only is it similar to the hydrogen 

 •curve, but by making two displacements parallel to the 

 coordinates it is found to be superimposable, and both 

 curves may be represented by a generalisation of Balmer's 

 formula, due to Rydberg, as follows : — 



N = A-B/(w + Mr, 

 where A, B and m are constants, B having sensibly the 

 same value as in Balmer's formula. 



It is interesting to compare the curves for the various 

 members of the alkaline metals among themselves, when 

 it is seen that both for the " principal " and the " sub- 

 ordinate " series the limits approach the red end of the 

 spectrum in the order of the atomic weights of the metals, 

 •as if the greater masses of the atoms caused the frequencies 

 of the vibrations to become less ; this same fact becomes 

 •obvious when we consider, similarly, the spectra of the 

 other metals classified into tReir natural groups. 



Prof. Fabry next describes the " satellites " which 

 accompany most lines in the several spectra. For an ex- 

 ample he takes the spectrum of mercury, which is com- 

 posed of triplets forming two series, one the " diffuse " 

 and the other the " sharp " (" first subordinate " and 

 " second subordinate " respectively) series of Rydberg. In 

 the "diffuse" series the first element of each group is 

 composed of four lines, the second of three and the third 

 of two, but in the " sharp " series the elements are 

 apparently single lines ; this is probably due, however, to 

 the very close proximity of the satellites in the latter series, 

 and in several cases MM. Fabry and Perot have shown 

 hat, with special apparatus having great resolving power, 

 these lines are of a compound nature, and have come to 

 the conclusion, which at least is probably the correct one, 

 that all the elements of the secondary series are accom- 

 panied by satellites. All these satellites appear to share 

 the common property of varying greatly under different 

 conditions of emission {e.g. as temperature, pressure and 

 nature of the electric discharge), and these two observers 

 have shown that, whereas the silver line at X 547-2, which 

 is a satellite of the line at X 5466, appears in the spark 

 spectrum in air, it completely disappears when the spark 

 takes place in vacuo. Many metals {e.g. Fe, Ni, Mn) 

 produce spectra so complex that, as yet, it has not been 

 possible to classify them, but this may be done when a 

 means of distinguishing analogous rays is discovered and 

 brought into use. 



This latter means may be found when the phenomena 

 first observed by Zeeman, and known as the " Zeeman 

 «ffect," have received a more complete study. This 

 •observer found that if the emission took place in a strong 

 magnetic field, each line was split up into a series of lines 

 symmetrically placed as regards the original line, but 

 differently polarised. Taking the spectrum of mercury as 

 an example, we see that the second subordinate series is 

 made up of triplets, or, as shown above, three separate 

 parallel series of lines, which one may call, in this explan- 

 ation, " a," " b " and " c " respectively. In the magnetic 

 field the members of the " a " series split up into nine 

 separate lines, four on each side of the original line, some 

 r.f which are polarised in the plane of the lines of force, the 

 others in the perpendicular plane, but the corresponding 

 line on each side is similarly polarised. In the " b " series 

 we get lines which are similarly placed as regards the 

 original line, and similarly polarised, but there are only 

 three on each side, the second member on each side in the 

 " a " group having disappeared. Similarly in the " c " 

 series only two extraordinary lines are seen, one on each 

 side of the original, corresponding to the extreme lines in 

 the " a " series. 



To the first workers in this field these lines appeared 

 jrreatly entangled, but, thanks to the labours of Cornu, 

 Micheison, Preston, and more especially Runge and 

 Paschen, order has been evolved from the chaos, and the 

 study of the " Zeeman effect " will, in the future, form a 

 ready means of recognising and determining series, for it 

 has already been proved that " the various lines which go 

 to make up similar series behave in an identical manner 



NO. I 76 I, VOL. 68] 



when the emission takes place in a magnetic field, and if 

 one represents each line by its ' frequency,' the various 

 members, in the same magnetic 5eld, resolve themselves 

 into groups which are strictly superimposable." It is also 

 to be hoped, and even expected, that when the work of 

 Humphreys and Mohler, and others, on the displacement 

 of spectral lines under various conditions of pressure, comes 

 to be further developed, similar laws as to the analogous 

 behaviour of lines in their corresponding series will be 

 evolved. 



Prof. F"abry concludes his article with a discussion of 

 the relations which exist between the absorption and 

 emission of the same radiations, taking the example of 

 the telluric absorption assigned to atmospheric oxygen in 

 the solar spectrum as an example for discussion. He 

 doubts the coincidence of these absorption bands with 

 emission lines in the spectrum of the gas, although, as 

 he points out, experimental means of proving their non- 

 coincidence have yet to be devised. 



CONGRESS OF THE SANITARY INSTITUTE. 



THE annual congress of the Sanitary Institute was held 

 at Bradford on July 7-1 1, under the presidency of the 

 Earl of Stamford. 



In his inaugural address Lord Stamford dealt with the 

 history of hygiene, showing how closely the subject was 

 allied to political, social and economic history. In de- 

 sctibing broadly the various sanitary questions as they 

 affected the home, factory, and the municipality, the presi- 

 dent dealt with the important subject of school hygiene, . 

 and pointed out how essential it was that the training 

 schools for teachers should form part of the coordinated 

 system of national education. It should be one of the first 

 requirements in the preparation of the teacher, and also of 

 the inspectors who are appointed to visit the schools, that 

 they should practically understand something of the nature 

 of the child material upon which they are to work, the con- 

 ditions under which the child can best develop by the 

 teacher's guidance, and the proper use of the appliances 

 provided in modern school buildings. 



The sections and conferences to which the papers and 

 discussions of the congress were allotted were presided over 

 by well-known representatives of different sciences connected 

 with hygiene. Prof. Clifford Allbutt, in his address on 

 sanitary science and preventive medicine, brought forward 

 for consideration the question if, within limits, the birth 

 of fewer children under improved conditions may be better 

 in the end than a more voluminous birth-rate of children 

 of which some may be of lower vital capacity, and many less 

 watchfully reared. 



Mr. Fitzmaurice, of the London County Council, presided 

 over the section of engineering and architecture, and in 

 connection with some of the large engineering works in 

 which he had been engaged he directed attention to the 

 duty of providing for the medical and sanitary requirements 

 of the large bodies of men temporarily collected for the 

 purpose of carrying out the works, and showed that atten- 

 tion to these requirements was an economic advantage. In 

 works like the Forth Bridge or others in the neighbourhood 

 of large towns the difficulty could be overcome, but in 

 works abroad, such as the Nile reservoir, the problem was 

 a more diflicult one, especially as smallpox and typhoid are 

 endemic in the Nile valley, and a large outbreak of either 

 in a camp where 15,000 persons were at times employed 

 would have been disastrous ; but by making careful pro- 

 visions, health conditions were so well maintained that, 

 during the five years the works were going on, there were 

 only four deaths from smallpox and one from typhoid fever. 

 He also dealt with the health aspects of cheap locomotion 

 to the suburbs, and motor traffic. 



Prof. Hunter Stewart, in addressing the section of 

 chemistry, physics, and biology, discussed the spread of and 

 immunity from Asiatic cholera, and referred to Great 

 Britain as the most striking instance of acquired immunity. 

 With a sea traffic from India greater than that of any other 

 European Power, and in constalnt communication with the 

 Mediterranean ports, with no quarantine and cordon regula- 

 tions such as prevailed on the continent of Europe, this 

 country has, since 1866, known cholera only in the sporadic 



