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SCIENCE 



[N. S. Vol. XXVIII. No. 713 



tween conjunction or opposition and quadra- 

 ture. The values assigned to the various con- 

 tributory phases are arbitrary, being merely 

 such as have resulted from a brief study of 

 the subject, and as such may be modified by 

 future observations. The efiect of conjunc- 

 tion seems to be a little less than that of 

 opposition, but I have given it the same value 

 as the latter; perigee is very powerful. I 

 have used the following values for the luni- 

 solar maxima: Opposition or conjunction 20 

 points, perigee 20, and half the actual degree 

 value of declination — for example : with moon 

 and sun in opposition, moon in perigee and 

 north and south declination 20°, the result 

 would be : Opposition 20, plus perigee 20, plus 

 declination 10, equals 50. If the moon were 

 in apogee the result would be 20 points less; 

 if the declination were zero the result would 

 be 10 points less, etc. 



For the terrestrial maxima, below the 

 medial zone, the values are the same but in- 

 versely applied, thus : quadrature 20, apogee 

 20 and zero declination 10 points. Declina- 

 tion differences in alignment of sun and moon 

 for opposition and conjunction are deducted 

 from the declination values. Difference and 

 supplement in right ascension and the right 

 ascension itself are neglected as being of 

 little importance, and no account has been 

 taken of the earth's perihelion passage nor of 

 the difference in power of sun and moon. The 

 declination values of quadrature are very diffi- 

 cult to assign and it is here that most of the 

 inaccuracy will be found — it is a problem 

 for the astronomer. When any maximum 

 occurs just before or after perigee the point of 

 the maximum is inclined toward the date of 

 perigee. The apogee-perigee values are taken 

 from sinuous curves traced within the medial 

 zone but which do not appear on the finished 

 chart. 



On the basis just outlined I have prepared 

 the accompanying curves for 1902, 1905, 1906, 

 1907 and 190S. In comparing these with some 

 volcanic phenomena occurring in these years 

 I have preferred^in order to avoid any pos- 

 sible personal bias — to quote from the pub- 

 lished observations of others, especially of that 



most accurate observer and indefatigable 

 student of Vesuvius, Prof. G. Merealli. 

 These observations were made by him without 

 consideration of astronomical influences and 

 were published before I hid made his ac- 

 quaintance. The accompanying curves were 

 made by me according to the above rules and 

 in ignorance of Mercalli's observations. 



Referring now to the chart for 1905, I will 

 translate from his " Notizie Vesuviane (anno 

 1905)," making only such excerpts as relate 

 to the greatest activity during each month. 



January : " In the night of the 25th and 

 26th the explosions took on a character purely 

 stromholian' with high projection of incan- 

 descent material (every four or five minutes)," 

 see (A) on chart. The reader will here wish 

 to ask why this did not occur on the date of 

 the first terrestrial maximum, which is more 

 accentuated than (A), but it should be noted 

 first, that (A) follows a strong luni-solar 

 maximum with which it forms a cycle, and it 

 should be remembered also that the active 

 periods we are now considering are compara- 

 tively unimportant and may be influenced by 

 local conditions — the interesting and funda- 

 mental fact is that even these occur on some 

 maximum of the curve. February: The ac- 

 tivity was quite uniform during this month, 

 but the culmination seems to have occurred on 

 the 22d, when the incandescence at the 

 crater — on other days spoken of as " sensible " 

 — is parenthesized as "rather strong." This 

 is close to (B). March: "On the 18th and 

 20th the incandescence was so vivid as to be 

 visible as far as Naples at 6 :45 p.m. while it 

 was yet day . . . the new interclosed conelet 

 . . . presented two points separated on the 

 west by a profound depression, where, during 

 the night of the 19th and 20th, I observed 

 permanent incandescence due to a small out- 

 flow of lava or at least to the elevation of the 



° Mercalli'a use of this term, now generally 

 adopted, signifies an emission of luminous ma- 

 terials, incandescent fragments and white vapors 

 as contrasted with " vulcanian " which indicates 

 the ejection of non-luminous bloclvs and bombs 

 with abundant detritus presenting the appearance 

 of black smoke. The terms are descriptive of the 

 character and not the force of the explosion. 



