13 
Vandloggen er, som man ser, en speciel Anvendelse 
88 , p 
af Pitot's Rør. Kaldes den Højde, hvortil Vandet stiger i 
Stigerøret over det Niveau, det indtager, naar Fartøjet 
g , Ser, ) 
ligger stille, 4, Skibets Hastighed v, Tyngdens Acceleration 
Bord » Mb, 8 » +yng 
g og er M en Coefficient, saa har man! 
EN 
0 = IM — 
29 
Coefficienten M har efter Dubuats Forsøg en Verdi, 
der er større end 1, men bliver mindre, naar Hastighederne 
bliver større, uden dog at naa Enheden. Ved en Hastighed 
af 1."8 pr. Secund fandtes M = 1.08. 
Ved Vandloggen, saaledes som den er indrettet af 
Lieutenant Petersen, er Coefficienten M sat lig 1. Rigtig- 
heden eller Tilstrækkeligheden af denne Antagelse til et- 
hvert praktisk Brug tilsøs, selv paa lange Rejser, er godtgjort 
ved den Anvendelse, Apparatet har havt paa *Vøringen” 
under 1877 og 1878 Aars Expeditioner og under dens Gang 
i Fragtfart paa Østersøen og Spanien, hvor lange Stræk- 
ninger er udsejlede uden Afbrydelse. Endvidere har det 
samme Resultat vist sig af Vandloggens Anvendelse paa 
Oplodningsdampskibet “Hansteen” hvert Aar siden 1875 
og paa Korvetten “Nornen” paa et Togt til Vestindien. 
Sættes Coefficienten M lig 1, Kvartmilen lig */;9 af en Ækva- 
torsgrad og g lig 9.”810 (509 N. Br.), saa faar man den 
følgende Tabel for Skalaens Inddeling. 
Fart. Skala. 
(Speed,) | (Scale.) 
Kvartmil 1 Timen. | Meter. 
(Miles an Hour.) 
(Aetres.) (Norw. Feet.) (Eng. Feet.) 
I 0.014 0.043 | 0.044 
2 0.054 0.172 0.178 
2.5 0.085 0.270 0.278 
0.122 0.388 0.400 
3.5 | O16 0.529 0.544 
4 | 0.217 0.690 0.711 
4.5 0.274 0.874 0.899 
5 ONS 1.079 Hol © 
BS 0.410 1.305 1.343 
6 | 0.487 1.553 1.599 
6.5 0.572 1.823 1.876 
" Bresse, Cours de mécanique appliquée. Seconde partie, p. 335. 
* Ved 80° Bredde med g = 9.830 bliver Skalastregen for 12 
Miles Fart 1.945 Meter, altsaa kun 4”” forskjellig fra Tabellens. For 
de mindre Hastigheder bliver Forskjellen forholdsvis mindre. 
Kvartmil i Timen. 
Norske Fod.| Eng. Fod. å 
The water-log is obviously a special adaptation of 
Pitot's tube. Let h be the height to which the water in 
the upper tube rises above its level when the ship is sta- 
tionary; v the speed of the vessel; g the acceleration of 
gravity; and M a coefficient, — we shall then have the 
formula ! 
32 
0 
lo = A og 
The coefficient M has, according to Dubuat, a value 
greater than 1, which diminishes however with increasing 
velocities, though without reaching unity. For a velocity 
of 1.”8 per second, the value of M was found to be 1.08. 
For the water-log on Lieutenant Petersen’s construc- 
tion, the coefficient M is put equal to 1. And this 
practically correct, even for comparatively long voyages, 
1S 
as shown from experience derived on the cruises of the 
*Vøringen” in 1877 and 1878, and on her voyages in the 
freight-trade to the Baltic and to Spain, very considerable 
distances having then been run at a stretch. Equally 
favourable results have been obtained, too, by the use of 
the water-log (since 1875) on board the Coast Survey 
steamer “Hansteen,” and on a cruise of the steam-corvette 
“Nornen” to the West Indies. Now, supposing the coet- 
ficient M to equal I, a mile to equal !/g of an equatorial 
degree, and g to equal 9.”810 (in lat. 50° N.), we have 
the following series of figures for graduating the scale. 
Fart. | Skala. 
(Speed.) | (Scate.) 
| Meter. Norske Fod.| Eng. Fod 
(Miles an Hour.) | (Metres,) (Norw. Feet.) (Eng. Feet.) 
7 | ©0038 | Aja, 2.176 
7.5 0.761 | DV 2.408 
8 0.866 2.761 2.842 
8.5 0.078 Bol AG 3.200 
9 1096 | 3.495 3.597 
9.5 B22 | 8804 4.008 
10 1884 || 453924 4.441 
10.5 | 1.492 | 4.756 4.896 
II 1.638 5.220 5.373 
Ti Hho} | 1.790 5.700 5.873 
iD” | 1.949 O.2 i 3 6.395 
' Bresse, Cours de mécanique appliquée. Seconde partie, p. 335. 
2 In lat. 80° N.. where g = 9.830, the division on the scale 
denoting a speed of 12 knots will correspond to 1.945, and thus 
exhibit a difference of only 4”” as compared with the figures in 
the Table. For less velocities, the difference will be proportionally 
reduced. 
