40 
Aneroid B. 
| 
Datum | | 
| N IL A 
(Date). | 
Aug. it Tt PRA 7.07 755.0" 
12 55:2 9.7 57.0 
14 56.9 Bo 2 59.9 
15 | 57-7 5- I 60.3 
16 56.1 5.5 58.8 
17 53-4 6.9 55-3 
18 53.0 8. 5 5595 
ne) 54.2 | 5. 6 56.5 
21 Glo 5.0 53.0 
22 49.4 | 6.8 51.5 
23 49.3 | 6.0 51.2 
Bi | A5).1 | 4.8 AT). 1 
N—A N == Al Obs. — Ber. 
obs. ber. (comp) (Obs. — Comp.) t 
OD | —2.10"™ SE Oy HP =| fo) 
— 1.8 — 1.8 0.0 I 
= HO — Eos == Oo) 3 
— 2.6 — 2.8 +o.2 Al 
— Dog — 2.6 — O.1I 5 
= 1.0) | — 2.2 + 0.3 6 
= UG) | = oO) 0.0 7 
— 2.3 | — 2.4 +o.r 8 
— 2.4 — 2.4 0.0 10 
— 2.1 | — 1.9 —0.2 I I 
= i) | = 240 | + 0.1 12 
== DO) | —2.0 | 0.0 13 
Formel (Formula): N= Å — 3.”"72 + 0.1801 7 + 0.0503 (760 — A) + 0.0129. 
i e= SF O71 77, 0 — SE (mm iS}. 
Aneroidbarometret B har herefter været meget tjen- 
ligt, og fuldkommen saa godt som Å. 
Sammenligningen mellem Styrmændenes og mine Af- 
lesninger af Aneroidbarometrene i 1878 giyer folgende 
Resultat. I Gjennemsnit have Styrmændene noteret 0.7002 
lavere end jeg, altsaa en umerkelig Forskjel. Den midlere 
Afvigelse mellem os er + 0.”"09 og den største er + 0.73. 
1878 Aars Barometerobservationer have saaledes i alle 
Henseender mindst ligesaa stor Sikkerhed som 1877 Aars. 
Efter disse Erfaringer om Aneroidbarometrenes Brug 
til Observationer tilsøs tør jeg trygt anbefale at bruge dem, 
under Forudsætning af, at der udøves en stadig Control 
med dem. Hurtig og bekvem Aflæsning med en tilstrække- 
lig Præeision (0.”"1), 1 alle Tilfælder, selv under meget op- 
rørt Hav, Lethed at anbringe paa et for Observator be- 
kvemt Sted, Følsomhed for Lufttrykkets Variationer ere 
Fordele. som Kviksølvbarometret ikke kan præstere 1 lige 
Grad som Aneroidbarometret ombord i et Skib. Den største 
Nojagtighed vindes ved at bruge Aneroidbarometret som 
Observations- og Variationsapparat, og, under dertil egnede 
Forhold, at bruge Kviksølvbarometret som absolut Lufttryks- 
maaler til Bestemmelse af Variationsapparatets Constanter 
og deres Variation med Tiden — samme Princip som ved 
Bestemmelsen af Jordmagnetismens Elementer. 
Ved Beregningen af Constanterne i Formelen for Aneroid- 
barometrets Reduction til Kviksølvbarometret har jeg ikke taget 
Hensyn til, at Aneroidbarometret maaler Lufttrykkets Variationer 
uafhængig af Tyngden, medens Kviksølvhøjden, ved samme absolute 
Lufttryk, er omvendt proportional med Tyngdens Størrelse. I For- 
melen skulde istedetfor N, den normale Barometerhøjde, staa Ud- 
The Aneroid barometer B proved, accordingly, a most 
serviceable instrument, and quite as good as Aneroid A. 
A comparison between the mates’ and my own read- 
ings of the Aneroid barometer in 1878, gave the following 
result. On an the mates were found to have 
noted 0.””002 lower than I — an imappreciable difference. 
The mean deviation between our notations is + 0.””09, 
and the greatest + 0.73. 
The barometric observations taken in 1878 have, there- 
fore, an accuracy quite as great as those taken in 1877. 
From the experience thus derived in the use of An- 
eroid barometers at sea, I can safely recommend these in- 
struments, provided they are submitted to constant control. 
Quick and easy reading, together with adequate precision 
(0.1) in all cases, even in boisterous weather, facility of 
mounting the instrument in a convenient place for the 
observer, sensibility to the variations of pressure, — such 
are the advantages in regard to which the mercury 
barometer cannot compare with the Aneroid on board a 
vessel at sea. The greatest accuracy is attained by using 
the Aneroid barometer as an apparatus for observing the 
variations of pressure, and by using, under favourable cir- 
cumstances, the mercury barometer to measure the absolute 
pressure for determining the constants of the variation ap- 
paratus, — the same principle, accordingly, as adopted for 
determining the elements of terrestrial magnetism. 
average, 
When computing the constants in the formula for the reduction 
of the Aneroid to the mercury barometer, I have not had regard to 
the circumstance, that the Aneroid measures the variations of pres- 
sure independently of gravity, whereas the height of the mercury 
with the same absolute pressure is in inverse proportion to the inten- 
sity of gravity. In the formula, instead of N, the normal height of thé 
