Clearly, you need a visa for two entries (which is not the same as a multiple-entry visa). You can specify that in box 24 but the form is not very well designed for this situation. I don't know exactly how you should proceed but the best I can think of is to provide all the documents for both trips and add a letter explaining why you applied for two entries instead of one. Official instructions don't particularly encourage it but nothing prevents you from doing that and I know some people who have had success explaining the particulars of their situation this way.
If that doesn't work and the Swiss consulates issues you a single entry visa, you can still apply for another visa once you're back in the UK. Two weeks is short but doable, especially if you have all the documentation from the first application at hand. Alternatively, if the first visa is set to expire before the date you intend to leave for Paris, you can also apply for the second visa from the French consulate in advance. As long as there is no overlap between them, there is no rule that forbids having several Schengen visas. Obviously, you would need to pay the fee again, which would be a shame, but at least you might still save your trip.