514 



NATURE 



[March 28, 1901 



way, and Mr. Knock's skill as an artist in portraying all 

 sorts and conditions of animal and plant life greatly add 

 to its charm. 



Elementary Organic Analysis. By F. G. Benedict, Ph.D. 



Pp. vi + 86. (Easton, Pa. : The Chemical Publishing 



Co., 1900.) Price i dollar. 

 Dr. Benedict describes processes for the determination 

 of carbon and hydrogen in organic analysis. His manual 

 is distinguished by completeness of detail concerning the 

 setting up and manipulation of the analytical apparatus, 

 and the treatment necessary for various classes of com- 

 pounds. The book should be of service in directing 

 students how to carry out organic combustions satis- 

 factorily. 



Elevation and Stadic Tables. By A. P. Davis. Pp. 42. 



(New York : J. Wiley and Sons. London : Chapman 



and Hall, 1901.) 

 Hydraulic tables showing velocities for various channels 

 and slopes are given in this volume, as well as tables 

 " for obtaining differences of altitude for all angles and 

 distances, horizontal distances in stadic work, &c., with 

 all necessary corrections." The book has been prepared 

 and published because there is a need for such a handy 

 manual in the field work of surveying and in practical 

 problems connected with canal construction. As such 

 its usefulness is assured. 



LETTERS TO THE EDITOR. 



I The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications.'^ 



The Recent "Blood Rains." 



The quantity of dust carried over to Europe by winds from 

 the African Continent during the present month seems to have 

 been unusually great, for traces of the " blood- rain " are said to 

 have been noticed as far north as Hamburg and Schleswig- 

 Holstein, while, in most cases, such phenomena are confined to 

 the countries immediately bordering the Mediterranean. My 

 colleague, Prof. A. W. Riicker, who has been staying at 

 Taormina, in Sicily, has forwarded to me some very interesting 

 observations which he has made on the subject. Writing on 

 March 12, he says : '* We have had a rather curious phenomenon 

 here. The sirocco was blowing, and the hills were wrapt in 

 mist, but the fog assumed a yellow hue, and the sun, which at 

 times could be seen through it, was a bright blue. This was 

 caused and accompanied by a copious fall of red dust. Some 

 which I shook off my hat was quite dry, and on looking at it 

 through a low-power lens all the granules seemed to be 

 spherical, except a very few grains of what looked like quartz. 

 Of course, the question was raised whether Etna was ejecting 

 something which corresponded to the Krakatoa dust, but this 

 was negatived by the fact that the Italian papers state that the 

 dust fell also at Naples and Palermo in such quantity that the 

 streets looked red and the people were frightened. I scraped 

 some off a marble table which I send you." 



Under the microscope this dust is seen to be mainly composed 

 of inorganic particles, chips of quartz in small quantities being 

 mingled with minute plates of various micaceous and other 

 minerals. There is also a fair admixture of frustules of fresh- 

 water diatomacese, entire and in fragments. The number and 

 variety of these diatomacese does not appear to be so striking as 

 in some of the celebrated cases described by Ehrenberg, the 

 organisms from which were figured by him in his " Passat Staub 

 und Blut Regen " (1847). There are, however, a very con- 

 siderable number of species represented in these recent falls. 



Vague statements have appeared in some of the newspapers 

 as to the number of millions of tons of dust which, during the 

 present month, have fallen over Italy. The data upon which 

 these statements have been made have not been given, so that the 

 following memorandum on the subject, drawn up by Prof. 

 Riicker, cannot fail to be of interest to readers of Nature. 



Royal College of Science. J. W. Judd. 



NO. 1639, VOL. 63] 



March 20, 1 901. Taormina, Sicily, 

 "At 7. 30 this morning the sky was copper-coloured, and it was 

 evident that another fall of dust was taking place. The sirocco 

 had been blowing for two days, and it was raining slightly. 



Hill behind 

 house 



House 



r terrace I. terrace II. 



62' 



The general outline of the hotel is as shown. The two 

 terraces are connected by a bridge. On the terraces were 

 several rectangular marble tables, and it occurred to me that it 

 might be interesting to find the amount of dust on some of 

 them. 



It is, of course, possible that the rain may have washed some 

 of the dust off them, but I looked at the terrace when dry and 

 saw no signs of a specially great aggregation of dust under the 

 tables. 



The aspect of the terrace is about S.W., so that the house 

 did not shelter the tables, as the wind was blowing towards it ; 

 but, of course, eddies may have had an effect. 



The sky ceased to be copper-coloured about 8 or 8.15, and I 

 have no reason to suppose that any large quantity of dust fell 

 while the experiments were being made. 



Table I. Was on the western half of the inner terrace I., 

 about 13' from the house. It measured 24^" x 46"= 1127 square 

 inches. The mingled dust and water were scraped off with the 

 edge of a sheet of paper into the cover of a biscuit box, then 

 dried over a spiritine (alcohol) flame. The dust adhered rather 

 strongly to the box, and had to be scraped off with a knife, 

 which removed some shavings of the tinning. 



Collection made at 9 a.m. 



Table II. Further east, on terrace I., near a point where the 

 level of the house fell to about 17'. Distance from house, 13'. 

 Dimension, 22V' x 4o4 "> or, say, 900 square inches. Collected as^ 

 before but into two plates, one earthenware, and the other 

 enamelled iron. The dust had to be scraped off, but I do not 

 think the knife removed anything from the plates. 



Collection made at 10.15 ^•™- 



Table III. This was the best experiment. The table was , 

 on the outer terrace, 58' from the house, and close to the edge of 

 the terrace. Area, 24!" x 46^" = Ii27"5 square inches. The 

 scrapers used were rags of clean muslin, which were afterwards 

 washed in water to get as much dust as possible out of them, 

 and the quantity so obtained (which was small) was added to- 

 the rest. The dust and water were put in a clean bottle and 

 preserved. No drying was done in this case. 



Collection made 10.45. 



In the afternoon I borrowed a balance from a photographer. 

 The smallest weight was a gram, but the balance would turn to- 

 less, and I made smaller weights by cutting a piece of stout 

 paper to such a length that it weighed a gram, measured its- 

 length and cut' off measured lengths from it. I weighed in both 

 pans and found there was no important difference. The whole 

 experiment was rough, but the amounts deposited on the two- 

 tables appear to have been so different that great accuracy ii> ^ 

 weighing is not important. 



Table I. Weight of dust, IT3 grams. 



Area, 1127 square inches, or, say, 



oooio gram per square inch. 

 Table II. Weight of dust, i "54 grams. 



Area, 900 square inches, or, say, 



o'coi7 gram per square inch. 

 Table III. Preserved wet, and therefore not weighed. 





