950 



SCIENCE. 



[N. S. Vol. XVI. No. 415. 



succeeding the nucleation is not as liigli as 

 before until the tenth, when a sudden enor- 

 mous increase occurs. The winds are here 

 again from the north and there is marked 

 fall of temperature. The high maximum is 

 succeeded by an equally low minimum brought 

 in by the rainy weather of the eleventh and 

 twelfth. The nucleation then rises in the 

 succeeding fair days, falls to a fourth mini- 

 mum during the rain of the fourteenth, and 

 then increases. 



ISTo doubt some fluctuation is due to varia- 

 tion of temperature for which no correction 

 was made,* but the rain and fair weather 

 effects, as a whole, are unmistakable. They 

 here correspond to periods of minimum and 

 maximum nucleation respectively. Moreover, 

 the maxima are associated with winds blow- 

 ing from the north in a general way, and at 

 times with sudden fall of temperature, while 

 the maxima of the fourth and tenth correspond 

 to anticyclonal conditions. 



6. Data Corrected for Temperature. — The 

 subsequent observations were improved by 

 aid of the water-bath, already mentioned, 

 kept at room temperature, so that the tem- 

 perature of the saturated air from which con- 

 densation takes place is fully known. The 

 corrections are made as will be shown else- 

 where. The final results are, at 



From these a table may be interpolated 

 showing the value of m for each degree of 

 temperature between 10° and 30°, and, there- 

 fore, the number of nuclei per cubic centi- 

 meter is 



Ji=24 X ms' X 10' 



for the observed value of temperature and 

 aperture, s. 



In this way the following observations were 

 corrected for temperature and the results are 

 constructed in the graph (middle figure), 



* As the air entered by a long pipe passing 

 through the room, the temperature variations were 

 probably within 5°C. The error so introduced is 

 not a serious quantity, as was found by direct 

 experiments subsequently made. 



beginning with October 14. Symbols refer- 

 ring to the weather and to other meteoro- 

 logical conditions are introduced as before 

 above the graph. 



7. Remarhs on the New Data. — With the 

 correction for temperature the curve has taken 

 a smoother form, showing the method to be 

 warranted; but the real cause of the differ- 

 ences of the two graphs is nevertheless due 

 to actual differences of nucleation. What is 

 particularly noteworthy is the occurrence of 

 sharp minima on October 16, 17, 21 and 23, 

 cotemporaneous with the passage of dense 

 cloud masses over the sky. On the 16th, 31»t 

 and 23d the curve rises as soon as the sky 

 clears; on the 17th this is not the case, but 

 the curve runs into the overcast conditions 

 of October 18. Another important feature 

 is the remarkably pronounced minimum of 

 nucleation on October 19, during clear 

 weather, showing that the presence of sun- 

 shine cannot be the sole reason for an abun- 

 dance of nuclei. The slight haze in the sky 

 may not be ineffective. Similarly there is 

 high nucleation on October 24 and 27, simul- 

 taneously with the overcast sky. A number 

 of night observations made after October 18 

 show no exceptional behavior. 



On October 27 the apparatus was again 

 modified as stated, by substituting a long 

 cylinder for the aspirator flask. Tests showed 

 the new results to be uniformly higher * than 

 the old, ccet. par., for which reason they are 

 separately given in the lower graph. 



The data begin with high nucleation under 

 an overcast sky and fall off to the rain storm 

 of October 28. From this they rise again to 

 values recalling the data of the early part of 

 the month. The high nucleatious are very 

 fluctuating, conditions which would be even 

 more apparent if night observations had been 

 made. The cause is obviously convection and 

 the diagram necessarily presents marked sim- 

 ilarity to a wind eurve.f The ascent on the 

 29th and the high values thereafter again 



*This is due to the uneven thicknesses of the 

 glass walls, a circiunstance which need not here 

 be considered.' 



t Cf . Langley, ' The Internal Work of the Wind,' 

 ' Smithsonian Contrib.,' 1893. 



