1886.] The Distribution of Micro-organisms in Air. 509 



The initial letters D, S, and Gr recall the origin of the earths 

 respectively from Didymium, Samarskite, and Gadolinite. 



The radiant-matter test applied to these phosphorescing bodies 

 proves itself to be every day more and more valuable, and one of 

 the most far-searching and trustworthy tools ever placed in the hands 

 of the experimental chemist. It is an exquisitely delicate test capable 

 of being applied to bodies which have been approximately separated, 

 but not yet completely isolated, by chemical means ; its delicacy is 

 unsurpassed even in the region of spectrum analysis ; its economy is 

 great, inasmuch as the test involves no destruction of the specimen, 

 and its convenience is such that any given specimen is always avail- 

 able for future reference. Likewise the quantity of material is limited 

 solely by the power of the human eye to see the body under examina- 

 tion. Beyond all these excellencies is its trustworthiness. I should 

 be exceeding the legitimate inference from experience were I to claim 

 that this test is infallible ; but this I may say — during the five years 

 in which this test has been in daily use in my laboratory. I never once 

 have been led to view its indications with suspicion. Anomalies and 

 apparent contradictions have cropped up in plenty ; but a little more 

 experiment has always shown that the anomalies were but finger-posts 

 pointing to fresh paths of discovery, and the contradictions were due 

 to my own erroneous interpretation of the facts before me. 



DESCRIPTION OF THE FIGURES. 



Fig. 1. — Absorption-spectrum of Didymium, showing the absence of the element 



forming the band X 443. 

 Fig. 2. — Absorption-spectrum hitherto ascribed to Didymium. 

 Fig. 3. — Absorption-spectrum of Didymium showing the concentration of the 



element forming the band X 443. 

 Fig. 4. — Absorption- spectrum of Dysprosium according to M. de Boisbaudran. 

 Fig. 5. — Absorption-spectrum showing the isolation of the band X451 *5, included 



by M. de Boisbaudran in the spectrum of Dysprosium. 



X. " The Distribution of Micro-organisms in Air." By Percy 

 F. Frankland, Ph.D., B.Sc.,F.C.S.,F.I.C., Assoc. Boy. Sch, 

 Mines. Communicated by E. Frankland, F.B.S. Received 

 June 7, 1886. 



The micro-organisms in air have formed the subject of investiga- 

 tions by Pasteur, Tyndall, Miquel, and many others. The researches 

 of these experimenters have shown that although these organisms are 

 most widely distributed throughout the accessible regions of the atmo- 

 sphere, yet that very marked differences do exist in the numbers 

 which are present in different places, and in the same places at 

 different times. 



