French to English Tech/Engineering Mathematics & Statistics Oceanography - Offshore construction

Dans le système absolu, les équations qui régissent le phénomène s'écrivent:

1. Continuité au sein du milieu ou équation de Laplace

Hello again. For those of you who answered my previous questions from this text, I have been doing lots of background reading and a terms which seems to crop up in roughly the same context as 'Continuité au sein du milieu' here is INTEGRABILITY. Does anyone know if this is definitly the same thing or am I barking up the wrong tree?

For those of you who are new to my seemingly ongoing oil-rig engineering related dilemmas, the text is a scientific paper on the estimation of wave and swell forces excerted on offshore structures. I'm in a little over my head (did you like the pun?!) with the physics and maths as I'm more of an environmental and earth scientist. As always any help welcome :)