146 



NA TURE 



[April 5, 1894 



<he same amount of haze when the air is very dry than when it is 

 dampish. It will also be noticed that the transparency of the air 

 is roughly proportional to the wet bulb depression. It should 

 r" noted that it is not the amount of vapour in the air that pro- 

 ducts this effect, but the nearness of the vapour to the dew 

 point which seems to enable the dust particles to condense more 

 vapour by surface attraction and otherw ise, and thus, by becoming 

 larger, they have a greater hazing effect. The above table 

 shdws the relation between the humidity, the dust, and the trans- 

 parenc"', so that knowing any two of them we can calculate 

 I he third. 



The paper then proceeds to an examination of the relation 

 between the dust and the haze from the Ben Nevis reports for 

 the periods of the Kingairloch observations, when it is seen 

 that on all days when the air was very clear the number of 

 particles was small at high and low levels, and the transparency 

 was least when the amount of dust was greatest. On one 

 occasion Ireland, which is 125 miles distant, was seen from Ben 

 Nevis, and only a thin haze was visible. On that day the 

 number was about 200 per cc. at low level, and under 200 at 

 high level, and, as the numbers remained very constant at both 

 levels all day, this day may be looked upon as one of the purest 

 as well as one of the clearest observed. 



The next set of observations discussed are those made 

 at Alford, in Aberdeenshire. The air at that station was 

 always very pure, except when the wind was southerly, and 

 brought impure air from the inhabited districts. The values 

 of C for the different humidities were calculated from the 

 Alford observations, and the results will be found in the follow- 

 ing table. When at Alford some observations were made on 

 Callievar, a hill about 1747 feet high. The values of C from 

 three observations made on Callievar do not agree with the 

 others, being only about one-half as great. 



The differtnce in the value of C obtained from the Callievar 

 observations opened up the question of the value of C as ob- 

 tained from observations at low level. The difference in the 

 two values might be due to the tests at low level being made in 

 locally impure air, near the surface of the earth, while the 

 estimates of haze are made partly through purer upper air, and in 

 calculating the value of C it is assumed that the air all through the 

 length in which the haze is estimated has the same amount of dust 

 as at low level, whereas it may have less. If, then, the low level 

 observations be made in polluted areas, they will give too high 

 a value for C. The difference between the amount of dust 

 at Kingairloch and Ben Nevis does not, however, account for 

 anything like the difference given by the Callievar observations. 

 As there were only three observations made on Callievar, it was 

 though) as well to test this point by working out the values of 

 C irom the Rigi observations. When this was done they were 

 found to be similar to those for the Kingairloch observations. 

 The following table shows the different values of C at the 

 different wet bulb depressions, calculated from the different sets 

 of observations : — 



Place. 



Kingairloch, 1893 

 1892 

 Alford . 

 Rigi Kulm 



Wet bulb depression. 



2° to 4° 4' to 7° 7° to 10' 



Mean 



77,000 



No observations 



75,000 



75,000 



76,000 



106,000 j 141,000 



117,000 175,000 



95,000 125,000 



104,000 124,000 



106,000 



141, coo 



What are called purifying areas in this paper are those regions 

 on the earth's surface in which the air lost s more impurity than 

 it gains. In all densely inhabited areas it loses its purity, and 

 in all uninhabited ones it tends to regain it ; but all unin- 

 habited areas are not equally good purifying ones. Much of the 

 dusty impurity discharged into our atmospheie from artificial 

 sources, by volcanoes, and by the disintegration of meteoric 

 matter, falls to the ground, but much of it is so fine it will hardly 

 settle. The deposition of vapour on these vei-y small particles 

 seems to be the method adopted by nature for cleansing them 

 away; they become centres of cloud particles, and ultimately 

 fall with the rain. It may be remarked that all very low numbers 



NO. 1275. VOL. 4Q] 



at Kingairloch were obtained in close misty rain, and in the 

 clouds near the earth, in the very area in which the dust was 

 being used up. This experience is confirmed by the observa- 

 tions made on Ben Nevis. From this it might be expected that 

 the areas where most clouds form, and most rain falls, will have 

 the greatest purifying influence. This conclusion is confirmed 

 by the dust observations made in air coming from four great 

 purifying areas, namely, the Mediterranean, the Alps, the High- 

 lands of Scotland, and the Atlantic. The following figures 

 show the mean values ot the lowest readings observed in each 

 of the five years in air coming from these areas ; the Mediter- 

 ranean, 891 per cc. ; the Alps, 381 ; the Highlands, 141 ; and 

 he Atlantic, 72. It should be noted that these are not the 

 mean numbers, but the mean of the lowest, and represent the 

 maximum purifying power of the different area~. 



UNI VERS IT V AND ED UCA TIONA L 

 INTELLIGENCE. 



The sixth summer meeting of University Extension and 

 other students will be held in Oxford from July 27 to August 24. 

 Courses of study are provided in numerous subjects of interest 

 and importance. Among the science courses are included lec- 

 tures on I'hysical problems relating to astronomy, by Dr. A. H. 

 Fison. Mr. Henry Balfour, Curator of the Pitt- Rivers Museum, 

 will lecture upon the arts of mankind and their evolution, illus- 

 trating his discourses by specimens exhibited in the museum. 

 Geology, both lectures and field work, has been undertaken by 

 Prof. A. H. Green, F.R.S. Dr. C. H. Wade will conduct 

 lectures and classes in hygiene, and Mr. J. E. Marsh have 

 charge of students in courses of practical chemistry at the 

 chemical laboratory in the University Museum. A lecture on 

 colour vision will also be given by Captain W. Abney. In 

 addition to these courses, and many others on history, litera- 

 ture, economics, and art, there will be a course on the science 

 and art of education, comprising lectures on psychology, the 

 theory of education, and the educational systems of England, 

 France, and Germany. Instruction in wood-carving, Sloyd, 

 and photography can also be obtained at the meeting. 



The Oxfoi-d University Extension Gazette announces that 

 the council of the London Society for the Extension of Univer- 

 sity Teaching has decided to hold in London, on June 22 and 

 23, a conference representative of all the authorities concerned 

 in the work of University Extension. The purpose of the 

 conference will be to sum up and present the educational results 

 of University Extension work since the inauguration of the 

 movement, and to discuss practical proposals and a general 

 policy for the future in the light of past experience. Official 

 representatives of the Universities of Oxford, Cambridge, and 

 London will be asked to preside over the three sessions of the 

 conference, which by emphasising the unity of the University 

 Extension system, will doubtless increase public interest in this 

 branch of educational work. 



SCIENTIFIC SERIALS. 



Bulletin de I' Academie Royale de Belgiqtte, No, I, — Anothei 

 word on the definition of latitude, by F. Folic. If a displace- 

 ment of the pole of inertia really exists, the difference between 

 the astronomical latitudes of two places situated upon opposite 

 meridians, such as Berlin and Honolulu, will be positive in 

 summer and negative in winter. It is therefore best to take as 

 a point of reference, not the instantaneous pole, but the mean 

 position of the pole of inertia, i.e. the geographical pole. As 

 regards the direction of displacement of the pole of inertia, M. 

 Folie's latest conclusion is that it is retrograde, wiih a period of 

 321 instead of 423 days. — Explanation of the systematic differ- 

 ences between the catalogues of Greenwich, Melliourne, and the 

 Cape, by diurnal nutation and the annual displacement of the 

 pole of inertia, by the same author. The hitherto unexplained 

 systematic differences between the three catalogues are elimin- 

 ated by the introduction of the constant term entering into the 

 expression for diurnal nutation. — A new gradual synthesis of 

 benzene, by Maurice Dclacre. This s)nthtsis starts, like the 

 one previously described, with acetophenone, and passes 

 through dypnone and dypnopinacone 10 the y varieties (not the 

 a bcries) ol dypnopinacoline, dypnopinalcohui, and dypnopin- 

 alcolene to triphenylbenzine. — Application of the refractometer 



