The New York herald., 1877-10-21
A VALUABLE INVENTION.
A COMPASS WHICH Is INsENsIBLE TO LOCAL
MAGNETISM.

COMPASS WHICH Is INSENSIBLE TO LOCAL
MAGNETISM
From the Wilmington (DeL) Commercial Oct. ISL
Mr. stephen Longiellow, OF Cambridge. Mass. now
OF ST. Louis. nephew Of Henry Longfeilow the poet,
has recently invented ships compass, designed 10
variations OF the needle local causes,
such the OF In construction or the carry
Ing OF large masses Of iron as cargo. Mr. Longieilow
was in the merchant service andin the navy many
years. and this compass the Of long study Of
the subject The bowl of the compass is surrounded
by tour magnets IN the form OF segmcnts, each seg-
ment one-slxth OF the circle They insulated by
means OF porcelain or glass knobs completely that
sx.pound magnet placed within very short dis
tance fails 10 affect them These magnetic segments
put IN slides around The upper part OF the bowl Of
the compass aud being attached to Jonted arms they
can be readily adjusted TO the plane oi the chord IN
compass. Their ordinary position IS IN the
plane Of the chord, extending around the
upper rim OF The bowl and distant there
from only about one-iourth Of an inch They prob
ably effect the same purpose thus placed as Professor
AIRY assigned TO effect when he recommended the
OF magnets paced near the compass and so ar
ranged to neutraze the influence OF all other local
attractionsj but the inventor claims that these
mental magnets are much more efficient than any ar
rangement OF magnets on the ships deck, or oil a
complete circle OF magnets designed TO neutralize
other local attractions one Of Mr.. Longielows
compasses has been made for him by optlcian Of
this city, and the needle shows practically deva-
ton when masses OF iron are near it, although
the same masses or IRON cause marked deviation IN
an ordinary compass Magnets were also used III an
experiment on the ELECTS oi local attraction with tho
same result u six-pound magnet witnn . few inches
Of the Longtenow compass failing TO defect the
needle. The segmentai magnets may be grouped
together 70 counter balance any extraordinary
attraction proving sufficiently great to aiect
the when the magnets are IN tuelr
normal position. but the inventor docs not anticipate
tnat there Will be necessity Tor calculations o de-
viations from local causes when his compass is usod
nor tor changing the position OF the magnets as ar
ranged IN corresponding positions around the rim oi
the bowl. The compass has many minor Improve
ments IN form and details over the ordinary ships
compass. The bowl Is not a true hemisphere but Is
shaped like an oblong acorn cup AMI mas u hollow
ball on the bottom, winch may bc weighted with shot
he spindle which the needle rests instead OF beng
iustened lead the bottom OF the bowl screwed
up through tue bottom with long bearings that IT
may be surely maintained III its vertical position. The
incosng shell whicn is designed TO protect the COM
pass from storms, ana tho lamps for nignt oDserva
tions also forms, but the chef feature OF
the compass is Its 0f segmenta insulated mag
nets Tor equallzng neutrallzng local attraction
II in practical trials II should do what its inventor
claims for IT, one great source OF marine disasters viii
be removed-the errors arising from unknown varia-
tions OF tho compass due TO local attraction.