New-York tribune., 1874-07-08
A CRITICISM on MR. PARKHURSTS ChLCU-
LAIIONS.

y CRl llClSM ON Nit. lAitIAIlJ 1 ltpl > N-ALNt
LATIONS.
WILL TIE COMETS TAIL STRIKE THE EARTH "A CUES
TIOS FOR MATHEMATICIANs.
To me EdttOr Of The TrtbUHe.
SIR: Having observed with no little inter
est the computations IN the columns Of THE TRIBUNE
i'm reference to the size and movements OF Cogsid
comet wish TO call the attention OF your readers To
some apparent discrepancies IN the calculations OF MI
Henry NJ Parkhurst in his letter OF July B. published IN
THE TRIBUNE Of July Mr.. ParShurst near tue close
OF his letter
Aermsny t. have found paric, Of the comets tai
winch pole dstuct from tue sun TO se Sue ,ait" ol
p smmHeI tier ittooc motions on Jav tat no
particle, can Il s0y than those truz ON hs caY
BY reference to the tabular statement OF distances,
&C. in the letter referred TO- hut tnatsMr Pdrkhurst
estimates the distance itself f-om the earth
ON the 4th of July TO be $1,000 miles that particles
must emanate fOm the comets head with force
sufficient TO carry them 5jOJO0) miles not inc!u ling
hyperbolIsm III order TO reach the earth at all This Is
equivalent stating that the comets tail, so far a. the
earth is concerned be- the Goth of Juy about
100000 miles length. Now supposing the present
length OF comets tail TO be 1OOOjOJJ miles (Which Is
a much higher estimate than any yet made) and sup
posing the actual Increase III length 10 be oue-tcnlh
day (as Mr. ParkhurS csm1te> the length Of the
tail GU the 10th OF July cannot DE quite 51,COO miles
Buj Mr.. PaTburst seems 10 have been under the lin
preston that If the tail ot the comet 2GOCjj miles IN
length ON Jlly ~ the edTth VIII ne IN the QUEER His o
tie tail. Thus III speaking ot Blcds comet ne states
that the earth passed directly through the heai Oi
"and the only effect a brilliant shower Of
meteors" We should hardly expect an equal tect from
passing through the tail OF comet the
head" He has thus apparently SeI"oheu HS dgt tl
when the comet at pergee, or 100000 miles distant
from the earth, the particles cnanaihg iro the hed OF
the comet on tat ddy Jdl ~ WI" 10 Tar Stdh' IToi
the earth at all points Of their passage aud when they
reach their ultimate destination; .,,,,
II Mr. Pdrkhurst estimates the length or the tail on
the q0th of july relatively 70 the earth, to be only
25O0OO miles, or little more ana also estimates tie
particles which reach the eaith az tat time 10 nave
emauated from the COMETS head lG days previous, he
must calculate that the PARTICLES move at the rate OF
I,625.0JO miles per day laII asuc tug ny PruVlisu
Bur as we have seen, on July the distance Of the
comets head from the earth was 55oOaOj0 miles. Divd
in- tins number ty l6AoVo ahu We nave 'he number A.
The number of days wncn must eaPse before the part
ces traverse the d,tauce winch me comet Is now
from the earth. 1hiS would carry the period when We
shall be IN the comets TAIL II al all, far into the
month of August. But assuming That the particles
which leave the hrad o the comet JAY
travel at the rate Of l6250O) niles per day mot eicu
lang the hyperbosin ad mat 10 10 days the particles
tbc head the length OF the tml which is to strike
July be only 21Cn 600 miles subtraciine this
number from 55.WOOO We OBTAIN ZyW1OOt, the actual
number OF miles which the end OF the tail Will be from
the EARTH Jdly 90 1s7i In other words according to
Mr. ParkhursIs own calculation, either toe earth VIII
moi be III the cOmcts tail until about the middle OF
August the end OF ls tai VIII never be nearer to
than .9OOO0 miles tlhoug OF course the mead OF the
comet aud some portions of II will be nearer than tha
ANA earth VIII not at any time be enyeloped ia the
The latter / am inclined TO believe to be the true
alternative. But the cause ot these discrepancies in Mr.
Pukhurss calculations seems 10 De IN confoundng the
distance the comets head from the earth July 20 with
the distance which the particles which reach the earth
M at am al that date traverse. Now, knows
letter than himself mat the particles cmaudtug from
tbe head OF "A at given time do titute
at that precise te, ana lhdt the particles
mating for instance, july 4, are not the particles
which reach their ultimate destination space on that
date THIS distinction Mr. Parkurs observes In makiug
certain computations but ignores in making
puatons. The tail OF comet consists of PARTICLES
emanating from tue head AT diherent pcrOdsperiOds
following each other with incalculable rapidiy. And
the particles Which reach the earth Of any cOus
tutc the extreme OF tail equal In length with the
distance the head Of the comet from tie
time those particles emauated from the head. II those
paricles left the head OF the comet July then the tail
which Is 10 strike must be jj,0ODJj miles in length
instead Of 26OOOOJO miles MT Parkhurst seems TO
suppose A. 4. sfKAGCE,
TrOJ n Y, july L. .S7i.