400 Notes and Memoranda. 



Sepaeating Powee oe Telescopes. — Mr. Dawes has a paper in Monthly 

 Notices which forms the introduction to his " Catalogue of Micrometrical Mea- 

 surements of Double Stars," in which he states that a telescope with one-inch 

 aperture will just separate two sixth magnitude stars, if their central distance 

 is 4". 56, and the atmosphere favourable. Hence the separating power of any- 

 given aperture, a, will be expressed by the position 4".56. According to this 



a •• 



formula a three-inch aperture should divide stars 1".52 apart ; a four-inch 

 1M4 ; a five-inch, 0".91 ; a six-inch, 0''.76 ; and a twelve-inch 0".3S0. These 

 calculations refer to refractors ; the finest reflectors, like Mr. With's mirrors, 

 probably have some advantage over refractors. 



Action oe Teees on Rainfall. — M. Becquerel states {Comptes Eendus), 

 that in wooded localities the maximum rainfall occurs in summer, and in non- 

 wooded localities in autumn. 



Teanspaeency oe Red-hot Teon. — In a communication of Father Secchi 

 to the French Academy, it is stated that a tube of forged iron was being con- 

 structed for a meteorograph, and he was afraid that the new tube might not 

 preserve a vacuum as accurately as one previously made. It was accordingly 

 made cherry red, almost white hot, and viewed in a dark place, when a slight 

 flaw was seen inside it. Father Secchi observes, " That red-hot iron is transpa- 

 rent to a depth of half a centimetre at least. 



Poisons oe Speeading Diseases. — Dr. Richardson has published in pamphlet 

 form* his lecture delivered before the Sewage Congress, in which he refers to an 

 observation of Dr. Salisbury during the American War, that a number of men 

 who slept on straw containing a certain mould or fungus, were seized with measles, 

 and he found that by inoculating himself and his family with the fungus, measles 

 was produced. Dr. Kennedy, of Dublin, is stated by Dr. Richardson to have 

 made similar observations. Dr. Richardson considers iodine as the best chemical 

 agent for destroying organic poisons. Iodine placed in a box covered with 

 muslin will diffuse itself at a temperature of 70°, at the rate of a drachm in 

 twenty-four hours. Heat and sunlight favour the destruction of the poisons. 



Aeeial Navigation. — At a meeting of the French Academy, 29 April, M. 

 Babinet spoke favourably of a machine invented by M. de Louvrie. The motive 

 power consisting of hydrocarbon vapour mixed with air, and exploded in a 

 cylinder having one circular opening. Twenty or thirty explosions per minute 

 were said to suffice. MM. Babinet, Piobert, and Delaunay were requested to 

 examine the apparatus and report upon it. Cosmos gives some further particulars 

 of remarks made by M. Babinet, and not printed in Comptes Rendus, from which 

 it appears that the apparatus is formed of an inclined plane, making a small angle 

 with the horizon, and moved horizontally by the reaction of a series of explosions 

 producing currents in the opposite direction. M. Louvrie has only made the 

 machine on a small scale, and M. Babinet wished the Academy to have a larger 

 one constructed. M. Flammarion (in Cosmos), describing the plan, says that a 

 kite, ten metres, each side formed of wire gauze, with the interstices filled with 

 gutta perch a, is to be solidly fixed to a car of thin copper, able to hold a man 

 lying down, and to contain a supply of the combustible liquid at its extremities. 

 The inclination of the plane of suspension is to be moved as required by wire 

 ropes, worked by an endless screw. At each end of the apparatus, cylinders of 

 steel are to be filled with a mixture of air and petroleum vapour, by means of a 

 pump, and exploded alternately by electric spark. From this description we 

 should not like to join M. Babinet in predicting the success of the* scheme. It 

 seems sure to fail. 



• Churchill aud Sons. 



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