Noble Intentions

22. Forebodings

When Gillian finished dressing, I led her to the chart room, released the clasps on a tall, narrow door and opened it. "This is the barometer, a delicate and fragile instrument, thus, the encasement and padding."

She examined it for a while, then asked, "How does this predict weather?"

"The tube is closed at one end, filled with mercury and inverted to stand with its open end immersed in this vented reservoir." I pointed to the glass bulb at the bottom of the case. "The weight of the mercury causes it to pull away from the top of the tube until its induced vacuum balances the weight of the atmosphere pressing down on the reservoir's surface."

Gillian nodded. "Why mercury?"

"Because of its weight. With it, the tube needs to be no more than three feet high. If we used water, we would need a column of over thirty feet."

She laughed. "Impractical. So, how do you interpret it?"

I pointed at the brass plate beside the upper part of the tube. "These numbers and graduations measure the atmosphere's pressure in inches of mercury. Above thirty is fair weather, and below it is increasingly foul."

"But that does not predict; it only confirms experience and observation."

"Ah, but the movement and its speed allow prediction. The more rapid the fall, the more severe the expected weather." I opened a book and pointed. "This morning, it stood at thirty point two."

She smiled and nodded. "And it is now twenty-nine point nine. What does this change mean?"

"Little at the moment. Fluctuating two points either side of thirty is normal. But if it continues down, we can expect clouds and rain." I wrote the time in the book and added the pressure beside it. "I will adjust my watch with sunset and record another reading."

"Adjust with sunset?"

"I have the time of sunset calculated and tabulated at all latitudes and for each degree of longitude in all navigable waters from London to Panama for every day of the year."

"Oh, my! But you said measuring longitude is imprecise."

"It is. But by factoring in the time of the sun's meridian passage, comparing the tables gives us a closer approximation." I pointed to sheaths and folders of paper. "I continue to refine the method, the reward being too much to ignore."

"Reward?"

"Four years ago, Parliament passed the Longitude Act, providing a prize to anyone who devises an accurate method. I had already begun cyphering and developing ideas, and the twenty-thousand-pound prize spurred me on."

"What? Twenty thousand? Surely not. That is a fortune of several lifetimes."

"Indeed, it is, and this shows how important its discovery is to the safety of navigation. My calculations on using lunar distance won me Doctor Halley's mentorship at Oxford."

"Your head must be full of figures."

I chuckled and turned, running my hands down the curves of her body and back up. "This figure, the most prominent among them."

A while later, when our mouths separated, she pressed Miss Cunny to the bulge down my thigh and said in a panting voice, "Barometer checked. May we now?"

"May we what?"

"Fuck."

Oh, dear, Lord! How hard to resist. But the ship ... "It might be best that you speak with Judith first. Learn how we may refine our method. Discover what will bring you greater pleasure."