Septemeer 14, 1905] 



NA TURE 



503 



Cape Colony, acting under the advice of Hutclifon, is 

 due the credit of proving that a preventive serum could 

 be prepared capable of immunising sheep against this 

 disease. Dr. Theiler informs me he has repeated Mr. 

 Spreuill's experiments, and they hope to introduce this 

 metho''' of inoculation at an early date. 



Heart-water of Cattle, Goats, and Sheep. 



This disease was also first clearly described by Mr. 

 Hutcheon. It occurs in the Transvaal, Natal, and Cape 

 Colony, and is responsible for much of the yearly loss 

 among the cattle, sheep, and goats. 



Like the last disease — Blue Tongue — it resembles Horse- 

 sickness in many ways, and, in fact, has been described 

 by Dr. Edington as being identical with it. Like Horse- 

 sickness, it is a blood disease with an invisible parasite, 

 so that blood injected under the skin of susceptible animals 

 gives rise to the disease. One difference between the 

 parasites of the two diseases is, that whereas that of 

 Horse-sickness is contained in the fluid of the blood, that 

 of Heart-water is probably restricted to the red blood 

 corpuscles. The serum separated from the blood is in- 

 capable of giving rise to the disease, and the straw- 

 coloured pericardial fluid, when injected into susceptible 

 animals, fails to give rise to any symptoms of the disease. 

 Horse-sickness blood filtered through a porcelain filter is 

 still infective ; the opposite holds good up to the present 

 with Heart-water. Horse-sickness blood can be kept for 

 years without losing its virulence ; Heart-water blood loses 

 it in forty-eight hours. 



Heart-water has a peculiar distribution, being restricted 

 to the certain tracts of country with a warm, moist 

 climate. It is known to farmers that if they remove their 

 flocks to the high veld the disease dies out. 



To Lounsbury is due the credit of explaining these facts. 

 He found that the disease is carried from sick to healthy 

 animals by means of the bont tick, Amblyomma hebraeum. 

 This tick leaves its host between each moulting, and a 

 larva which sucks the blood of an infected animal is 

 capable of giving rise to the disease in a susceptible animal 

 either as a nvnipha or imago. The distribution of this 

 tick corresponds to the distribution of the disease. If 

 this tick could be killed off, the disease would disappear 

 from the country. This could doubtless be done on in- 

 dividual farms by long-continued dipping ; but in the 

 meantime son-e method of immunisation might be devised. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



The next session at the South-Eastern Agricultural 

 College, Wye, will commence on Monday, October 2, when 

 an address will be given by Prof. Marshall Ward, F.R.S. 



The new session of King's College will be opened on 

 October 3, when an address will be delivered by Prof. 

 Clifford Allbutt, F.R.S., on " Medical Education in 

 London." On October 4 an inaugural lecture will be given 

 by Prof. Arthur Dendy on " The Study of Zoology." 



The inquiry into the general conditions of the home 

 life of the Berlin brass-workers, their education and trade 

 conaitions, which the small party of Birmingham delegates 

 carried out last April, is embodied in an interesting and 

 entertaining manner in a report recently issued — " The 

 Brass-workers of Berlin and of Birmingham," bv 

 Messrs. R. H. Best, W. J. Davies, and C. Perk's 

 (P. S. King and Son, price is.). The sensible inferences 

 and criticisms contained in the report are ample evidences 

 of close and accurate observation. The net practical con- 

 clusion of the inquiry seems to be that so long as the 

 Birmingham brass-worker confines himself to the repro- 

 duction of a number of plain models, his work, especially 

 his polished brass-work, is excellent, both in price and in 

 finish ; but " the Berlin training schools have produced 

 a class of artisans with artistic talent, who find ready 

 employment and are of great assistance to the employers. 

 ... A proper apprenticeship to his trade has fitted him 

 (the Berlin brass-worker) and placed him in a position to 

 supply the internal construction of intricate work without 

 every minute detail being put down for him on paper. 



NO. 1872, VOL. 72] 



In the bronzing and treatment of the finish a greater 

 freedom is apparent and a greater variety and novelty"; 

 in fact, " they lead the way, we follow. ..." The moral 

 is obvious; indeed, in the further discussion of this point 

 we find what is undoubtedly the most generally applicable 

 and valuable criticism in the whole report : — " It is on 

 the intellectual side that Birmingham requires to adapt 

 itself to changed conditions : not to cheapening its wares 

 but to getting more conception into them." 



SOCIETIES AND ACADEMIES. 



London. 



Royal society, April 13.- 'The Amplitude o, the Mini- 

 mum Audible Impulsive Sound." By Dr. P. E. Shaw. 



In a previous paper {Phil. Mag., December, igoo) the 

 author found this quantity by direct measurement, and 

 Rayleigh, Franke, Toepler, and Boltzmann have investi- 

 gated the minimum audible for continuous sound. In each 

 of the above researches the micrometer was not sensitive 

 enough actually to measure the least audible amplitude ; 

 the relation of current to amplitude was determined for 

 relatively large amplitudes, and separate measurements 

 were made of the current which gives the least audible 

 sound. Extrapolation then gives the amplitude in question. 



The present paper shows how the amplitude can be 

 measured directly without extrapolation ; it is even 

 possible, as shown in the tables, to measure movements 

 the amplitude of which is too small to be audible. The 

 instrument is the improved electric micrometer described 

 at the Royal Society (see p. 495), which is capable of 

 showing a movement of 0-4 fifi. 



There are two distinct parts in the determination: — 

 (i) Observe the position of the diaphragm of a telephone 

 when at rest, by making electric contact ; draw away the 

 measuring point of the micrometer and pass a steady 

 current through the telephone so as to move the diaphragm 

 to a new position of rest. Now move up the measuring 

 point to the diaphragm, watching the micrometer screw 

 and listening to the contact. Thus measure the move- 

 ment of the diaphragm due to a set of steady currents 

 down to such small ones as cause imperceptible motion. 

 Plot the relation between movement and current. 



(2) Apply the ear to the telephone and pass through it 

 the same set of currents as before. For each current, 

 except the smallest, a sound is heard when the current is 

 stopped. We thus learn the relation of current to audi- 

 bility. 



The curve above at once gives the relation of amplitude 

 to audibility. The sound is impulsive, for the diaphragm 

 is released from a position of strain, vibrates under great 

 damping, and soon comes to rest. 



Both right and left ear of the author were used. He 

 found, averaging results, 07 fi/j. as result for the right 

 ear, and 09 /x/x for the left. 



The fundamental of the diaphragm when clamped hard 

 to the case was found by testing it against tuning forks 

 to have frequency about :;So. 



The following table of amplitudes is given : — 



A B 



Just audible 



Iu>t romforfablv loud 



Juct uncomfortably loud 



Just overpowerinc 

 The word " just " here implies in each case the lower 

 limit. The amplitude of the diaphragm must not be con- 

 fused with that of the air which it vibrates. Lord 

 Rayleigh obtained the relation between these amplitudes 

 to be roughly 5 to i. 



Column .\ gives numbers actually found in the tele- 

 phone, and using Rayleigh 's factor we obtain column B 

 for the corresponding amplitude of the air. 



It should be observed that 014 fi/j. is the smallest audible 

 amplitude for an expectant ear when the conditions as to 

 silence are exceptionally favourable ; yet 10 fx,/i is the 

 amplitude for the smallest audible sound in air, about 

 which the ear can be quite sure when the conditions are 

 normally favourable, and the ear not listening for the 

 sound. 



From the results found the author calculates the ampli- 



