June 2, 1892] 



NA rURE 



1 1 



The average age at election was 43-9, and the average age of 

 all the Feljo'v.s in 189 1 was 58 '4. 



Table III. records the numbers of Ordinary Fellows elected 

 in each year, and remaining alive in each year afler election, 

 until 1 89 1. 



From this it will be seen that during the last ten years the 

 numbers have increased by 46 ; in the previous ten years the 

 increase was 68, or 22 more ; and in the ten years still earlier 

 the increase was in, or 43 more than the last. If the decrease 

 of growth for the ten years after 1890 takes place in a similar 

 ratio to that which took place between 1870-80 and 1880-90, 

 we might anticipate an increase of only 11 up to 1900, or 

 probably a smaller number. 



Tn order to obtain a satisfactory comparison between the lives 

 of the Fellows, and those of the general population as shown in 

 the accepted life tables, I have calculated, from the known ages 

 of the Fellows at election, and the known dates of the deaths 

 that have occurred among them, the average age of the Fellows 

 remaining alive in each year. From these ages I have computed, 

 from Dr. Farr's tables, the probable number of Fellows that 

 would survive from year to year, assuming the initial number to 

 be 15. 



From Table III., above referred to, has been ascertained the 

 number of Fellows surviving in each successive year after election, 

 and thence has been obtained the average number surviving 

 from an initial number 15. 



The results of these computations will be found in Table IV. 



The second column in this table sh )ws the number of lives 

 dealt with for each year after election. The first entry, 645, is 

 the total number of Fellows elected in the whole 43 years. The 

 next column to the right gives their aggregate ages, and the 

 next their average age, 44*9, in iheir first year. Following the 

 same line to the right, we find the average number of Fellows 

 elected, and in their first year. 



Passing to the second line of the table, 619, immediately below 

 645, is the total number of Fellows remaining in their second 

 year from the elections of 42 years ; this is succeeded, in the 

 columns to the right, by their aggregate ages in their second 

 year and their average age, and the average number in their 

 second year, out of 15, the average number elected. 



The third line gives the same data for the third year of 

 Fellowship, and so on throughout, the last line but one showing 

 that in their 42nd year there remained 6 Fellows from the 

 elections of 2 years, with an aggregate age of 444 years, and an 

 average age of 74 o, the average number surviving in their 42nd 

 year, out of the 15 elected, being 3. 



The sixth column of the table gives the successive sums 

 of the numbers in the fifth column, and therefore indicates 

 the aggregate number of Fellows that will, on the average, be 

 surviving in each successive year of Fellowship, the number 

 elected in each year being always supposed to be 15. 



It will be seen that the total for the 43rd year is 397 "o, 

 whereas the actual number surviving, shown in column XI., is 

 401. This difference is of course due to the number 397 re- 

 presenting what the result would be if the average rates of 

 election and decrease prevailed, instead of the actual rates for 

 the separate years ; and it is probably sufficiently accounted for 

 by the fact, already pointed out, of the gradually increasing age 

 at election in the later years, which will lead to the lives in the 

 earlier years of the series beinj; somewhat belter than the 

 average. Column XI. shows the actual results for successive 

 years corresponding to the average results given in column VI. 

 The differences will be seen to be somewhat irregular, but 

 nowhere to be of importance. 



Column VII. gives the aggregate ages of the numbers surviv- 

 ing in successive years, as shown in column V., and from it is 

 deduced the average age of the whole number of Fellows shown 

 in column VI., 397, which is seen to be 577 years, a result 

 differing slightly from that obtained from the actual ages of the 

 Fellows surviving in 1891, which was shown to be 58"4. The 

 cause of this difference has already been indicated. 



Columns VIII. and IX. supply the results that would be 

 obtained by applying to an initial number of 15, the rates of 

 mortality in Dr. Farr's tables, for the ages in successive years 

 given in column IV. Column X. contams the ratio of column 

 VI. to column IX., and indicates that through >ut the whole 

 period of 43 years the actual results are somewhat better than 

 the tabular results, or that the lives of the Fellows are better 

 than the ordinary lives, and that this advantage leads in the 

 43rd year to the actual number of survivors being rather more 



NO. I 179, VOL. 46] 



than 5 per cent, in excess of that which would be given by ihe 

 life tables, or of about 20 on a total of 400. 



An examination of this table will show that, with the excep 

 tion of the last six or eight year', in which the number ol lives 

 dtalt with at last becomes very small, the figures mdicate a very 

 regular and consistent j rogression, and ii will practically be 

 quite safe to assume that the series in column VI. may lie ex- 

 tended on the basis of the ordinary life tables, subject to the 

 addition of 5 per cent, on the total amounts obtained from tlif.se 

 last. 



Hence it will be found that in 10 years after 1891 the apgie- 

 gate number of Fellows is not at all likely to be increased by 

 more than 15, that the final rcMilt u ay be as little as 410, but is 

 not likely to be more than 420, or at the outside 425. 



In an earlier p.-irt of this paper, I mentioned that the rate of 

 decrease of the Ordinary Fellows elected before 1848 did not 

 appear to differ materially from that which has prevailed subse- 

 quently. 



Taking the number of Ordinary Fellows elected before 1848, 

 and then alive, at 718, it will be found that in 12 years (i860) 

 the number was reduced to 422, which is about 60 per cent, of 

 the original number ; after 24 years (1872) the number fell to 

 206, which is about 30 per cent, of the original ; and in 36 

 years (1884) there remained only 65, which is about 9 per cent, 

 of the first number. 



Assuming that the average age of the 718 Fellows elected 

 before 1848, and then alive, wa- not materially different from 

 (58) the average age of the Fellows elected after 1848 and alive 

 in 1891, when it has probably become nearly stationary, it may 

 be inferred that the lap-es among a boHy of Fellows of that age 

 will correspond to the lapses among the Fellows aWve in 1848. 

 Now, from Table IV, it will be seen that of the Fellows elected 

 after 1848, the average age in their 17th year was 58'3 >ears, 

 which is almost exactly the average age of the whole body. 

 Further, it is shown that of the supposed original 15 there 

 remained 10 9 in the 17th year of the age above mentioned, 58*3. 

 This number was reduced in 12 years to 67, which is nearly 60 

 per cent, of the number in the 17th year, and again falls after 12 

 years more to 37, which is not very different from 30 per cent, 

 of the starting number, and after 12 years more the number will 

 be seen to be likely to be less than i "o, which again will not 

 differ materially from 9 per cent, of the original 10*9. These 

 proportions, it will have been observed, are those above shown 

 to hold in the case of the Fellows elected before 1848. 



On the whole, it seems to be established that the present 

 restriction to 15 of the number of Ordinary Fellows elected 

 in any year will lead to an eventual maximum number not 

 exceeding 420 ; and that the ultimate increase of the total 

 strength of the Society, for each additional Fellow elected in 

 excess of 15 may be taken at 28, so that an increase to 18 

 of the annual number of Ordinary Fellows elected would lead to 

 an ultimate total of 500 such Fellows. 



THE ERUPTIONS OF VULCANO 

 {AUGUST 3, 1888, TO MARCH 22, 1890).! 

 'T' HERE are some 180 (nominally 212) pages and ii plates. 

 ■*■ Of these latter 4 are reproductions of Silvestri's beautiful 

 whole-plate photographs [one of Vulcano at rest (*ith Vulcan- 

 ello), and the other three instantaneous views of the volcano in 

 eruption]. A fifth reproduces, half-size, two of Dr. Johnston- 

 Lavis's instantaneous views of eruptions taken from the crater's 

 edge." Two other plates give 14 excellent photographs of 

 the "bombs," and of the rest two are sketches of Stromboli 

 crater, one petrographical, and the last the map of Vulcano 

 (1/50,000). 



I " Le Eniiione dell' Isola di Vulcano, incominciate il 3 agosto, 1888, e ter- 

 minate il 22 Marzo, 1S90: Relaz.one scientifica delta Commissione incaricata 

 degli studi dal R Governo," AnnalideW UfficioCentralc di Meteorologicae 

 Geodinamica, Parte 4, vol. .\., 1888 (Rome, 1891). 



The Commission was originally as follows : — President, Prof. O. Silvestri 

 (Catania). Prof. G.* Mercalli (Milan), Prof. Grablovitz (Seismological Obser- 

 vatory, Ischia), and as engineer, V. Clerici (Mestina), with A. Cerati, Prof 

 Ponte. and A. Silvestri, as assistants. 



As is known, Prof. Silvestri died before the publication of ihe Report, but 

 not till some months after the end of the eruptions, on which he had else- 

 where published various papers. The Commission must thus have had full 

 time to profit by his exrerienceboth in the field and afterwards, and his name 

 appears as author or joint author of a number of sections, .\fter Silvestri's 

 death. Prof Mercalli, the largest contributor to this Report, took his place, 

 and brought the work to its completion. 



» For others bv Dr. I..avis and Silvestri, see " South Italian Volcanoes." 



