J. D. Dana — Summit Crater of Mt. Loa. 85 



ber, April, April, March, and the number for the same months 

 of the year becomes 20 or 21 out of 27.* 



Full meteorological tables for a comparison of the months 

 as to precipitation, both at the base and summit of the mountain, 

 do not exist, and the discussion of this important question has, 

 therefore, to be left unfinished. 



I have received the following notes on the snows of Mt. 

 Loa in a recent letter from Mr. J. S Emerson of the Hawaiian 

 Government Survey. "The snow-cap of Mt. Loa in general 

 may be considered as making its first appearance in the early 

 part of JS1 ovember, and as lasting until late into March. This 

 is my impression from observations the past season, which 

 I think has not been particularly exceptional. During the 

 early part of November the snow-fall was quite light, and 

 seemed to melt rapidly away at its lower edges. By the 

 25th there had been two heavy snow-storms covering the 

 mountain top with a thick coat, which lasted all through 

 the winter. The snows are usually the heaviest in the month 

 of February, I think, though I did not see the mountain dur- 

 ing that month this year. My last view of Mt. Loa was on 

 March 29th, when I could just distinguish patches or streaks of 

 snow on the more protected portions of the summit." 



The relation to barometric changes is an important subject 

 for future study, with respect to which we have now no knowl- 

 edge. There are also variations in the amount of vapors over 

 the active craters dependent on hygrometric changes to be in- 

 vestigated. 



In view of the above facts it is probable that if there is any 

 periodicity in eruptions, it is more or less dependent on meteor- 

 ological cycles. 



3. Variations in activity since 1843. — The copiousness of 

 the subaerial discharges has diminished greatly since 1859. 

 Before the end of that year, or in the 17 years from 1843 to 1860, 

 five of the eight great eruptions had occurred ; and of the 

 three in the following 27 years, only one, that of 1880-81, was 

 of great length. 



The frequent occurrence of the brilliant summit displays 

 during the twelve years preceding the middle of 1880 is an- 

 other striking fact. Six cases are reported, and one was pro- 

 longed with small interruptions for eighteen months. 



The first of these displays occurred nearly 4J- years after the 

 eruption of 1868. But Mr. Coan, the mountain chronicler, 

 was absent in this country during one year in the interval — 

 from the spring of 1870 to that of 1871. After the summit- 

 display of August, 1872, they came at short intervals, their 



* This relation to the seasons, first recognized by Mr. Coan, is mentioned also 

 by Mr. Green in his Vestiges etc., p. 332. 



