May, 1915. 



KNOWLEDGE. 



155 



the filament is then adjusted until the filament is of the same 

 intensity as the source. It is now assumed that the tem- 

 peratures of the source and filament are the same, and in 

 order to standardise the instrument it is necessary to find 

 the connection between the current through the filament 

 and its temperature. This may be done by using several 

 standard temperatures in an experimental furnace, the 

 standards being the known melting-points of various pure 

 substances. On the other hand, one could calibrate the 

 instrument from observations on a suitably constructed air- 

 thermometer, the bulb of which is placed in the experimental 

 furnace. 



It will be noticed that with total radiation pyrometers and 

 with optical pyrometers the observations are taken on the 

 interiors of enclosures, the walls of which are at practically 

 the same temperature throughout. If such instruments 

 are directed on to the glowing surface of a crucible of molten 

 metal freely exposed to the laboratory, the reading for the 

 temperature would be too low, because the radiating surface 

 is not black, nor does it behave as black, in a radiation sense, 

 unless it is totally enclosed in opaque walls at the same 

 temperature. 



A NEW PRINCIPLE IN OPTICAL PYROMETRY.— 



Paterson and Dudding recently read a paper entitled " The 

 Estimation of High Temperatures by the Method of Colour 

 Identity " before the Physical Society of London. In this 

 paper the authors introduce an entirely new principle into 

 optical pyrometry. Their method of temperature measure- 

 ment is based on the physical discovery- that, when a body 

 is radiating in the open, and not in an enclosure at a uniform 

 temperature, the colour of the light emitted (in the visible 

 spectrum) may be identical with the colour emitted by a 

 black body, even though the total radiation over the visible 

 spectrum is less than that due to a black body. Such 

 sources of light may be appropriately termed " grey," and 

 Paterson and Dudding's method may be summarised by 

 stating that the temperatures of " grey " bodies are identical 

 with those of black bodies when the tint of the light is the 

 same. 



The comparison of colour is made similarly to photo- 

 metric comparisons of intensity. In the practice of the 

 method the intensity adjustment is also carried out, al- 

 though no readings of the photometer bench are taken. 

 The readings actually recorded are the values of the current 

 in the comparison glow lamp. In order to convert these 

 readings into temperatures it is necessary to find the 

 temperatures of the filament by other means, as in the case 

 of the Holborn-Kurlbaum pyrometer. 



THE AEOLIAN HARP.— This instrument offers several 

 interesting problems, which have not, up to the present, 

 been completely solved. In general appearance it resembles 

 the monochord of the instrument-maker, and consists of 

 a sound box, 3-ft. long, 5-in. wide, and 3-in. deep, made 

 of pine, with hardwood ends to hold the tuning pins and 

 hitch pins. A dozen or so of gut strings of different thick- 

 nesses, stretched rather slackly over the bridges near each end 

 of the sounding-board, are tuned in unison. The sounding- 

 board is provided with two rose holes, like those of a violin. 

 A long funnel is formed of an upper board, which rests an inch 

 or two over the strings on projections from the hardwood 

 ends, and of an extension laterally of the sounding-board. 

 The harp is placed on the window-sill, and the lower sash 

 drawn down on to the top of the funnel. With moderate 

 wind the sounds are pleasing, but when the wind i too 

 violent, shrill discords result. 



Rayleigh has already dealt with the subject, and now 

 returns to it in a paper entitled " Aeolian Tones" m The 

 Philosophical Magazine for April. 1915. He has shown that 

 the vibrations of the strings are transverse to the wind, and 

 has subjected the matter to mathematical analysis Some 

 of the results have been further tested by experiments on 

 motion in air and by observations on a pendulum suspended 

 in moving water. 



RADIO-ACTIVITY. 



By Alexander Fleck, B.Sc. 



ANNUAL REPORT OF THE RADIUM INSTITUTE 

 — The report of the work accomplished by this institute 

 during 1914 has just been published. The first few pages 

 are devoted to a description of the form in which the radium 

 is used, the screens with which it is covered, and the length 

 of time during which the active material should be applied. 

 A short account is also given of the results that should be 

 looked for by different exposures to the rays, and the various 

 factors which influence these results are also stated. The 

 greater part of the report is, however, occupied in enumer- 

 ating the various diseases which have been treated, and 

 discussing the results obtained, with a detailed description 

 of a large number of typical cases. The report concludes 

 with a short account of the work of the chemico-physical 

 laboratory of the Institute, which shows that its work is 

 extending rapidly, and in many instances the requirements 

 during 1914 have been three or four times as great as those 

 of 1913. 



Although the record of 1914 does not disclose any epoch- 

 making results in the treatment and cure of malignant 

 disease, it can at least be said that steady progress is being 

 made in the better use and control of the energy and pro- 

 perties of radium. 



A NEW METHOD OF RADIUM THERAPY— A 

 number of papers by Dr. W. C. Stevenson, of Dublin, have 

 appeared during the past months in various medical 

 journals describing one method which has been used in that 

 city for the medical use of radium emanation. The essen- 

 tially new feature of this method is that the radium 

 emanation is sealed into capillary tubes of 0-76 millimetre 

 external diameter. These tubes are then fixed with wax 

 inside hollow needles of one millimetre external diameter, 

 which are very similar to the needles of a hypodermic 

 syringe. The great advantage of them is that they can be 

 insetted into a tumour with comparatively little pain to the 

 patient, and without the use of an anaesthetic. As fifty 

 millecuries of emanation can be placed in one inch of the 

 capillary tube, and as six needles can be inserted in one 

 moderately sized tumour, it is evident that the dosage of 

 radium can be varied at will over a large range. There is 

 also the additional advantage that the whole of any desired 

 region can be radiated much more uniformly than is possible 

 with one supply placed at one point. 



THORIUM CONTENT OF THE EARTHS CRUST. 



A paper is contributed by J. H. Poole to the April number 



of The Philosophical Magazine on this subject. It gives the 

 results of the analysis (by radio-active methods) of the 

 thorium content of a large number of acid, intermediate, 

 and basic igneous rocks. The method employed is a com- 

 parative one, described by Joly a number of years ago, in 

 which the activity of the short-lived emanation is measured. 

 The results of the work are (1) The more acid an igneous 

 rock is, the more thorium it is likely to contain [2 the 

 average content of a gramme of granite is 2 ; 

 grammes of thorium, and of a gramme of 

 0-56 x 10- 5 grammes of thorium; (3) the mean value of 

 the thorium content of the earth's crust is probably 

 mimes per gramme . and ■ is no 



constant relation between the amount- oil radium and 

 thorium in igneous rocks, and consequently there is no 

 evidence, so far as this work goes, of a genetic com. 

 between thorium and radium. 



ZOOLOGY. 



By Professor J. Arthur Thomson. M a , LLP 



\N ISHMAELITE IBEX.— Dr. John C Phillips reports 

 on the Sinai Ibex [Copra >.-:< much per- 



secuted species, which is found over all the ragged parts of 



