304 



SCIENTIFIC NE^VS. 



[Mar. 30, I? 



of " thinking on his feet.'' When laying, ^^o-., any new 

 discovery before a society not only the ideas but the very 

 words have to be elaborated beforehand, so that nothing 

 may be open to misunderstanding or mis-interpretation. 

 Old and New Astronomy. By Richard A. Proctor. London : 

 Longmans, Green, and Co. Part L Price 2S. 6d. 

 The first section of this work, which will be completed 

 in twelve parts, now lies before us. The greater portion 

 of it is devoted to a description of the ancient and 

 modern methods of observing the heavenly bodies. As 

 might be expected, the astronomical character of the 

 great pyramid receives considerable attention, and an 

 account of the ancient observatories of Delhi and Benares 

 is given. Astrolabes and other ancient instruments are 

 briefly alluded to, and the different varieties of the modern 

 telescope are fully dealt with. The work is printed in 

 large type, and is profusely illustrated. From the 

 prospectus we learn that this volume is intended to 

 present in a popular form the latest ideas of physical 

 astronomy, and as we are sure the author will do justice 

 to the subject, we can strongly recommend this work to 

 our readers. 



A Treatise on Mathematical Instntments, their Construction, 

 Adjustment, Testing, and Use Concisely Explained. By 

 J. F. Heather, M.A. Revised, with additions, by 

 Arthur T. Walmisley, M.LC. E. London : Crosby, 

 Lockwood, and Son. Price 2s. 



The fact that this work has reached its fourteenth 

 edition is sure evidence that it is greatly appreciated. 

 Mr. Walmisley's appendix brings the information up to 

 date, and amongst the most recent forms of instruments 

 described are Amsler's planimeter, Hedley's dial, Abney's 

 level, Cassell's pocket altazimuth, and a variety of range 

 finders. A few notes on photography are also added, 

 but as photography is now so much used in copying 

 plans and preparing the blocks from which they are 

 printed, we think a little more space might be devoted 

 to this subject with advantage. 



We can cordially recommend this work to those in- 

 terested in the use of mathematical, optical, surveying, or 

 astronomical instruments. 

 Thejournalof the Franklin Institute. Vol. cxxv. No. 747. 



Among the more important matter in this number we 

 notice a paper on " Heating Cities by Steam," a subject 

 to which the present severe season lends exceptional in- 

 terest. To have an entire city warmed to such a degree 

 that its streets could never be blocked by snow-drifts, or 

 rendered dangerous by shot-ice — glass-bottle, as it is 

 called in North England — would be indeed a triumph. 

 But wherever practicable it would surely be better to 

 bore into the earth until hot water is reached, and let 

 this circulate through the streets. Professor E. J. Houston 

 discusses the Paillard " non-magnetic watch," in which 

 an alloy is substituted for steel in the balance and springs. 

 My Telescope, and some Objects which it shows me. A 

 Simple Introduction to the Glories of the Heavens. 

 By A Quekett Club Man. London : Roper and 

 Drowley, 1888. Price 2s. 6d. 



This is a simply written little introduction to the study 

 of the heavenly bodies. It contains a very brief de- 

 scription of a telescope, and short accounts of the sun, 

 moon, planets, star clusters, nebulae, and coloured stars. 

 It is illustrated with ten plates, but, unfortunately, they 

 are so roughly drawn that they convey but little idea of 

 the objects themselves. 



THE ENUMERATION OF ORGANISMS 

 IN THE AIR. 



THE determination of the number of micro-organisms 

 in a certain quantity of air has attracted the atten- 

 tion of many investigators. This is owing to sickness 

 and death in man and animals being traceable to the 

 existence of these germs. Twenty-seven years ago 

 Pasteur used a very simple appliance to determine their 

 number. He prepared several hermetically sealed 

 flasks, of definite size, containing small quantities of 

 a nutritive liquid, from which the air had been 

 expelled by boiling. On breaking off the sealed 

 end a certain quantity of air rushed into the flask, 

 carrying with it the micro-organisms which it contained. 

 The flask was then resealed, and if any microbes had been 

 carried in, their presence would in due course be ob- 

 served. Out of twenty such flasks which Pasteur 

 exposed in the country at a distance from all towns or 

 villages, eight, after suitable incubation, showed altera- 

 tions, which indicated the presence of the germs. Out of 

 twenty flasks, into which air from the Jura mountains 

 was admitted, five became contaminated, and out of 

 twenty flasks exposed in the Montanvert, at a height of 

 6,500 feet, only one became infected. 



Eleven years ago Tyndall adopted a different method 

 to ascertain the same result. He constructed a square 

 table provided with 100 small openings, in each of which 

 was fixed a test-tube, containing nutritive fluid, which 

 had been properly " sterilised," or deprived of all germs 

 by heat. Tnis set of tubes was daily watched, being 

 open at the top to admit the air and its contents. He 

 observed that the tubes did not all make the same 

 change ; that the changes took place at different times, 

 dependent on the position of the tube ; and that these 

 changes varied according to the particular kind of or- 

 ganism with which the individual tube had become 

 infected. 



Three years ago, MM. Freudenreich and Miquel at the 

 Montsouris Observatory, Paris, further elaborated pro- 

 cesses for the quantitative estimation of the micro- 

 organisms in the atmosphere. They aspirated a definite 

 volume of air through a plug of sterilised glass-wool, 

 which was then agitated with a definite volume of 

 sterilised water, so as to distribute the collected organisms 

 in the water. The water was then divided into a number 

 of equal parts, each of which was added to a flask con- 

 taining sterilised nutritive liquid. The volume of water 

 with which the plug was agitated was so selected that 

 when divided into the given number of equal parts, the 

 micro-organisms were so attenuated that only a part of 

 the whole number of inoculated flasks became infected. 

 Owing to that circumstance they argued that the organisms 

 had been very widely distributed in the water. 



In 1881, Koch first applied a solid nutritive 

 medium to the examination of air for microbes by ex- 

 posing glass slides, on which was the solid — peptone- 

 gelatine, potatoes, etc. On that surface the micro- 

 organisms were deposited from the air ; these germs 

 were suitably incubated, and the colonies of organisms 

 were counted and examined. 



Koch's method was a new departure in the examina- 

 tion of air. It was further developed by Hesse, who, by 

 gently aspirating air through wide glass tubes (30 inches 

 long, and i| inches diameter), which had been previously 

 coated internally with peptone-gelatine, found that the 

 I whole of the micro-organisms were deposited on the walls 



