New-York tribune., 1870-08-19
MODERN SCIENCE.

RO-MAGNET1SM-LAKE JSOTHERNALS-THE
AURORA BoREALIs-TERREsTRIAL MAGNET
sM-THE SUNS AURoRAL ACTION.
Troy, Aug. 17.-Though not fully prepared,
the Association proceeded with the predetermined pro-
grnmne this afternoon, and shortly after O'clock tho
body divided into two deliberatiye sections, working
simultaneously and in separate apartments Section A.
presided by the learned and vigorous Prof f. A. p
Barnard OF New York. meets In the large hall OF Mrs.
Willards Seminary. and Section b. with the noted Prof
Asa Gray OF Cambridge, sits in the City Hail. general
assembly is held each day preliminary TO tho
division OF the sections. whereat such gen.
eral work is done Ia suggested by the ext
gencies OF tho hour. Section A, which has to deal
with those special branches connected mathematics
and the physical sciences shortly after o'clock took up
a paper treating "Dsperson and the Possibility OF
Attaining Aehromatism" read by Prof r. C. Pickering
somwhat noted New-Engand scholar. One OF the prin
cipal defects in tho achromatc lens Ia the secondary
spectrum. color which remains with even the best
glasses II spectra obtained with prsms Of different
materials the colors found TO occupy unequal por-
tons of them Thus in one the red Ia predominant in
another blue Hence neutrazing one color does not
make others disappear. AZ this IL inherent In the
nature of the substances IL commonly supposed To DC
without remedy. we apply Cauchys formulas for dis
person 10 the expression the deviation OF ray, we
find that this deviation is independent OF the wave
length, ia the same for all colors, when simple
condition Is fulfilled. curve was next shown,
I'm which horizontal distance gave wave lengths
three lines solar spectrum b. F, and give points
almost precisely edudstan while their intensity and po-
ston at the and middle OF the spectrum
very suitable for observation The formulas were ap
piled 10 the observations OF Fraunhofer Dale and Glad
stone The cause Of the mperecon OF the common achro
matte lens is very obvious the curve corresponding
crown glass is nearly a straight lne that to flint glass
paraboa. II makers OF lenses when introducing new
kind of glass would its index OF refraction our
knowledge OF this subject would be greatly EXTENDED
The glass should be cut into prism. the ndices OF re-
fraction measured for the line In the extreme red IN
the blue and in the violet. simple calculation then
gives the equation and any two substances are found
fulfilling the conditions mentioned above they VIII form
lens giving mag ges almost perfectly free from color.
The second paper the Isohermals Of the Lake Region,
read by Prof. wnchell provoked earnest debate The
paper embodied the results OF careful and prolonged
observation various localities in the region west OF the
great lakes as far as Nebraska The Professor used in
the illustration Of the subject nine sotherma charts Tor
several of the Summer months and Winter Autumn and
Spring year mean minima and extreme minima. Ihe
professor indicated the wonderful changes in tempera-
ture caused by the great lakes in the contiguous country
The cooling influence science atess, exerted chiefly on
side of Lake Michigan and the warm on te east
which depends againupOn the prevailing Wlnds IN
along the shores OF the from the east Of the meridian
i'm Summer, and west OF it in Winter In july Tor ek-
tbe soterm9is 10 niles while to the west of the lake
they detected 400 miles In January the mean te-
peraure the east side OF the lake s from four 10 SIX
degrees higher than the west side The l5othefnals
for Spring show marked cooling influence exerted on
the west side and those for the Autumn warming IN
Huence the east side, the joint effect OF whch IS 10
render the growing season six to thirteen Say longer % %
most marked effect and the most surprising , IL
felt in times OF extreme weather, especially II cold The
literally norb and south along the shore OF Lake
greater than at Fort Riley in Kansas, 40 miles further
ycar The soSermSs Of the year might be expected
TO show resultant OF lake lnuehtts' & o On ,I0 I'm in
inences excited the east side this because the liquid
temperture above tbat Of the contiguous gO anu tSc
water The great depth Of the Lake 900 fee is sufficient en-
IS degrees of inereased the
of the lake would result in an equal ana average
ton OF Temperature sufficient to cause inc phchOnen'
Prof A. NJ Mayer OF the Lehigh University read pa
nor an "Researches i'm Electro Magnesm." in which he
deyeIoned delicate and precise method Of measuring and
comparing the forces OF heles ahd OF eleeto,Idghee
which passes the current from battery, so that
similar poles Of the helices are opposed while Det%eeh
brought TO such position that stands at o. when the
battery circuit opened or closed Ihus can De
and measured difference IN me forces OF lne e9i OF "a
he hclces OF OOOth part The paper presented
the results Of elaborate researches Win ~ te & ped
Wiz Comparison of the relative lorces o cocs ~
of insulated and uninsuated wires deterhihiLoh oI
whtS wnt on an eecromagnet core formed OF tube
slit longtudinaIy; and many other lnNestigIohs Vl
viii he of some value the constructors or telegraph
annaratus in afording them means OF measuring ana
Mr. HIssrd Of the u Coast Survey remarked that
he REGARDED this method Of Prof Mayer as OF great
( value, as giving precise means OF measuring the
strength eleetromagnets in the lines used IN Dc
prof Hough of the Dudley Observatory made rev
se Of Pro Mayer O e%
CUSTOM indicating more the interest oi tne % Il
the theories OF Prof Mayer, followed rnueu, ro
LOOMS OF the chair of Natural Philosophy In Yale read
interesting paper on Sb I 5be tne pnmbr
observed each year ana the @ eN.G oi nm ,l
spots on the surface OF M the snn upop 6e
surface have been carefully observed III Europe upoI
every day when the weather %oEd np mn m
observations extend back to the time OF the inventor
70 assign in numbers the relative extent OF the suns
spotted surface with great accuracy for eacn year since
tnries These observations clearly indicate successive
maxima and xima In the extent OF the suns spotted
which vary from to IA years the average nterya
being exactly 10 years aGeordlng & 70 iloi' hOOi
Similar periodical changes have been observed IN ane
daily rang Of the % tse pestest
in Europe the past 80 years, and similar thougn r
accurate observations extend back aDout cehFlI l
These observations clearly show that the mean day
snge OF the magnetic needle has periodical
VARYING IN e 70 Minutes The average interval be-
tween the successive maxima Is almost e3he3 ~ tb
tbose @ Of The ma 1i, the solar spots We nnda ir s
periodicy in the dlsPsys o, d ne erjca II is believed
middle %, tho hdhcy latitudes auroral displays
Una veil ~ nigh incessant IN all years and that IN mos re-
i he neriodicy shown IN the variation Oh pillh
glos s pn in the frequency of the displays but ny
Combining observations made near Boston anI e and
NJ, Nh .he resutng number exhibit alternate akna anu
mnms, whose periods correspond in rentAaDe MAJ he o1
nnr With the periods OF the solar sPots aho tne
,s ntI o., the magnetic needle Similar re1t' afSVp
,tned ~ we compare the condition or the shs surface
,ar few days preceding and few days oa9H e one OF
,bee nerlod the magnetic needle suffers renarka
lie aisrbances and those are now commonly Known as
magnetic storms. At Greenwich about ten sch days on
an sverage occur each year BY comparing the condition
o me suns surface upon the SIX days preceding anu o