Alexandria gazette. [volume] (Alexandria, D.C.) 1834-1974, 1877-10-23
a Valuable Invention.

| Nj. Stephen Long follow, Of Cambridge
| Mass, now Of st. Louis nephew OF Honr,
Longftlow, the poet, has recently invonted
| ships compass, designed to overcome variation
| Of tho needle due to locsl Causes. such as tn
use tf iron in construction, or the carrying c
| largo masses Of iron az cargo. Mr.. Longielop
| was in tho merchant service and in tho navy fo
| many years, and this compass Is tho result o
| long study of the subject. The bowl Of The aom
pass is surrounded by four magnets in the form
Of segmants, each segment onesixIh OF tho circle
| They arc insulated By means Of porcelain o.
| glass knobs SO completely that six pound mag
| net placed within very short distance fails IL
affect them. Theeo magnetic segmcnts are pu
| in slides around tho upper part Of the bowl o
| tho compass, and being attached to Jonted
arms they can DO readily adjusted TO the plano
cl The chord in q broken circle,or grouped TO-
gether ON one side of the compass. Their ord
nary position is in the plano Of the chord, OK
tending around the upper rim OF the bowl and
distant therefrom only about one fourth oil al
inch. They probably effect the same purpose
thus placed as Professor Airy designed 10 effect
when he recommended the use Of magnet:
glazed near the compass and 80 arranged as tc
neutraiZs the influence of all other local sttrac.
lions but tho inventor claims that; these seq
10 entail magnets are much moro efficient than
any arrangement Of magnets on the ships deck
or of q complete circle of magnets designed u
ncutruize other local attractions. Ono OF MIR.
I.ongfcllows compassos has beon made for him
by an optician OF this city. AID tho noodle show;
practically no deviation when masses of iron are
brought noar it, although tho Same masses CT
iron cause marked deviation in an ordinary
compass. Magnets were also used IN an experl
mont on tho effects Of local attraction with the
samo result, six pound magnet within few
inches of the Lougfellow compass failing TO de-
fleet the noodle. Tho scgmental magnets IN ~
DO grouped together to counterbalance any eI.
trsordnary attraction proving sufficiently groat
to effect the compass when the magnets are in
their normal position. but the inventor does not
anticipate that there will be any necessity Tor
calculations of devia!ons from local causes when
his compass is used, nor for changing tho posi-
ton ofthe magnets 40 arranged in correspond
ing positions around tho rim Of the bowl. Iho
compass has many minor improvements IN form
and details over tho ordinary ships compass;
Tho bowl is not true Hemisphere but is shaped
ON tho bottom, which may be wolghtc1 with
shot Tho spindle on which the needle rosts
instead Of being fastened in load at the bottom
cGthe bowl is screwed up through the bottom with
long bearings so that it may DO surely main
tsinel lis vertical position. The enclosing shell
which is designed to protect the compass from
storms, and tho lamps for night observations arc
also of now froms, but The chief feature OF the
new compass is its uso in segmental insulated
magnets for cqualiZlng or neutra!lzlng local at
traction. lin practical trials it should DO what
lis inventor claims for it, one great source OF
marine disasters will BIO removed-the errots
arising from unknown variations of the compass
dueto local attraction Wilmington (Del) Com
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