GEOPNEDSEPNE DISS XV 
ONNES (H. KAMERLINGH.). v. KAMERLINGH Onnzs (H.). 
ORDER of exception (Multiple umbilics as singularities of the first) on point-general 
surfaces, 386, 
ORGAN-FORMATION (An investigation on polarity and) with Caulerpa prolifera, 420. 
ORGAN-PIPES (On the relative sensitiveness of the human ear for tones of different 
pitch, measured by means of), 549. 
ORIONIS (Dispersion bands in the spectra of 5) and Nova Persei. 323. 
ORTHONITROBENZYLTOLUIDINE (On). 666. 
OSCILLATIONS of the solar activity and the climate. 368. 
OSCILLATORY DEFLECTIONS (On a new method of damping) of a galvanometer. 315. 
OSMOTIC PRESSURE (On the) of the blood and urine of fishes. 537. 
— (A formula for the) in concentrated solutions whose vapour follows the gas laws. 723. 
— (Kinetic derivation of vaN ’T HoFF’s law for the) in a dilute solution. 729. 
— and thermodynamic potential. 741. 
OUDEMANS (ce. A. J. A). On Leptostroma austriacum Oud., a hitherto unknown 
Leptostromacea living on the needles of Pinus austriaca; and on Hymenopsis 
Typhae (Fuck.) Sacc., a hitherto insufficiently described Tuberculariacea, occurring 
on the withered leafsheaths of Typha latifolia, 206. 
— On Sclerotiopsis pityophila (Corda) Oud., a Sphaeropsidea occurring on the 
needles of Pinus silvestris. 211. 
OUDEMANS (J. A. C.) presents a paper of S. Brok: “The connection between the 
primary triangulation of South Sumatra and that of the West Coast of 
Sumatra’. 453, 
— Determinations of latitude and azimuth, made in 1396—99, 482. 
— A short account of the determination of the longitude of St. Denis (Island of 
Réunion) executed in 1874. 602. 
OXYDATION (On the intramolecular) of a SH-group bound to benzol by an ortho- 
standing NO,-group. 63. 
PEKELHARING (c. A.) presents a paper of Dr. M. C, DEKHUIJZEN ; “On the 
osmotic pressure of the blood and urine of fishes”. 537. 
— presents a paper of Dr, W. Hurskamp: “On the presence of fibringlobulin in 
fibrinogen solutions”. 610. 
PENCIL (The locus of the principal axes of a) of quadratic surfaces, 341. 
— (The equations by which the locus of the principal axes of a) of quadratic 
surfaces is determined. 532. 
— (The equation of order nine representing the locus of the principal axes of a) 
of quadratic surfaces, 721. 
PERIOD (On a twenty-six-day) in daily means of the barometric height. 18. 
PERITHECIUM (On the development of the) of Monascus purpureus Went and Monascus 
Barkeri Dang. 83. 
PHALANGISTA VULPINA (On the genital cords of). 87. 
PHASES (The derivation of the formuia which gives the relation between the concen- 
tration of coexisting) for binary mixtures. 156, 
