The Nitrogen Fix

By Hal Clement

Something terrible happened in the past. Somehow, Earth's atmosphere has lost most of its oxygen and life on Earth has been devastated. Now the only animal life left are a few struggling settlements of humans. There is plant life, of a sort, and people are able to survive by maintaining greenhouses full of crops and plants that provide food and oxygen. But life is very harsh and life spans greatly shortened.
Kahvi and Earrin are nomadic traders, traveling by raft to and from seaside communities. They have a young daughter and Kahvi is pregnant. They have a small greenhouse in which they sleep and recharge their oxygen equipment. They also have a traveling companion, Bones.
Although Kahvi and Earrin are sure they are the aliens and Bones is the native, the reverse is the actual truth. Bones is an observer from another star system, on Earth to study its native life and atmosphere.
A group of young scientists from the former city of Boston has developed the hypothesis that Bones and his fellow aliens on Earth are the ones responsible for the destruction of the oxygen as part of a plot to seize the world for themselves. To that end, they have captured a small alien and are now attempting to capture Bones. They don't know that the aliens are mere observers and are on Earth just to gather information. But Kahvi and Earrin have known Bones for years and trust the alien, even leaving it to watch over their young daughter.
It all comes to a head when the radicals take not only Bones but Earrin too and Kahvi has to try to save both her husband and Bones from the well-meaning but mistaken young scientists.

I liked this book. It paints a picture of a very different world in which people are barely managing to hang on, a real survivor tale, with the added interest of strange, peculiar aliens. The humans have made science a forbidden subject, blaming it for the collapse of the atmosphere. The young scientists in the story are revolutionaries, going against the established wisdom in order to attempt to save their damaged world. And even though they are the "bad guys," at least they are trying to do something, unlike their elders. Very interesting and exciting story.

Cycle of Fire

By Hal Clement

Dar was on a delivery mission when he ran into trouble and was forced to make a crash landing. He managed to land safely but his aircraft was defunct. He removed his cargo, a bag of books, and proceeded to continue his mission on foot.
Dar lived on a large planet with two suns. The two suns created a cycle of conditions in which the planet gradually became too hot. So Dar's people packed all their knowledge away in the coldest spot on their planet, under the glaciers, safe for when the cycle reversed and the planet began to cool off and became more moderate again. This cycle meant that almost everyone faced certain death, including Dar, except for a few individuals, the Teachers, who resided with the books of knowledge under the glaciers.
Dar was making his way across a brutal, uninhabited and increasing hot landscape when he came across something he had never seen before: a human being. Nils Kruger was just a cadet when he fell into the mudpot and sank from sight. His fellow explorers assumed he was dead so they returned to their spacecraft and left without him. But Nils wasn't dead, he managed to drag himself out of the mudpot only to find he had been abandoned, left alone to survived on a hostile world. Through trial and error he managed to find plants that were edible and get by. But he was all alone when his and Dar's paths crossed. Finding each other to be non-hostile and desirous of heading to the same place, Dar to place his precious books into safe storage and Nils to find a place where the temperatures were more moderate and bearable for a human, they traveled together, headed to the land of glaciers.

This was an OK story. It started out pretty good, with the two traveling together and getting to know and understand each other. The author doesn't go into much detail about the plants and animals they encountered, which was disappointing. Also I didn't find the circumstances of Nils being stranded very believable. Then in the last half of the book, the adventure part ends and the rest of the story was just not that interesting. And there was a lot of scientific stuff in the last half of the book about how the planet ended up with two suns that I didn't understand, it was just too technical. I just skimmed those parts.

Still River

By Hal Clement

A mixed group of young scientists consisting of one human woman and four nonhumans are sent to the planet Enigma for what is, in effect, their final exam for what we would call their doctorates. The planet is called Enigma because it is very small, too small to retain its atmosphere, but it does. The young scientists must determine why Enigma has an atmosphere.
From the get-go there are problems. While Enigma has an atmosphere, since it is small, it hasn't much gravity. But it does have wind, as Joe, the first scientist off the ship, discovers when he is quickly blown away. Fortunately, he was unharmed as was the next person to run afoul of Enigma's treacherous environment, Carol, who was briefly buried in a sand pit. What the scientists didn't know was that the numerous sand pits on the surface of Enigma were bottomless, with sand blown by the gale force surface winds and into an extensive network of caves and tunnels.
Joe has designed a group of levitating robots meant to track Enigma's wind patterns. But one of the robots ends up down in the cave system and Molly (the only human), trying to reclaim the robot, falls way down into the cave system too. She latches on to the robot because its power supply can also power her space suit. She can't stop the robot from travelling with the cave winds because her fingers are too big to reach inside the control panel. (Joe, who built the robots, is a tiny creature compared to Molly.) So she has no choice but to go where the robot takes her and hope that her teammates are able to effect a rescue. So everyone puts their planned research aside in order to figure out how to find Molly in the extensive labyrinth of caves with which the planet is riddled.

The main thing I liked about this story is the interactions between the members of the team. All of the are different species and of an assortment of body types consisting of a human, a small humanoid, a centipede-like being, and two spherical beings, one small and one large. Despite their differences and occasional misunderstandings and a few disasters, they manage to come together to save Molly and Carol and even figure out the riddle of Enigma.
The traverse through the cave system of Enigma was less interesting. The book has a lot of physics and chemistry and I think someone who understood that stuff better than I do would get a lot more from the story than I did. At times it seemed like the story would never reach its conclusion, as Molly and Carol wandered endlessly through the dark, monotonous caves. Also, for a bunch of people in line for advanced degrees, they sure made a lot of stupid mistakes! But, overall, I think I liked the story pretty well, Enigma is a strange and interesting place and I liked the characters.

Mission of Gravity

By Hal Clement

Mesklin is a huge, cold planet with liquid methane seas and crushing gravity from three to 700 times that of Earth, depending on where you were on the surface, with the lightest gravity at the equator and the heaviest at the poles.
Inhospitable to human life, still Mesklin is not a barren planet. It teams with plants and animals and also has intelligent denizens who are not technologically advanced.
Humans have a scientific outpost on a moon of Mesklin and have sent a survey rocket down to the poles. It is the only rocket they have that is designed to withstand the tremendous pressure it will encounter there. But something has gone wrong and the rocket, which apparently landed as intended, is not responding to their communications.
Fortunately, a scientist at a station on the planet's equator (the only location where a human can survive the planet's gravity since it is only three times that of Earth's there) has established friendly relations with a few the natives of the planet, a group of intrepid explorers and traders. Led by their captain, Barlennan, they have agreed to travel to the pole and, with the advice of the humans, attempt to salvage the rocket's mission. But this will be a journey of thousands of miles, across strange territory, inhabited by unknown perils. Why would Barlennan and his crew undertake such a risky and dangerous expedition? Because they want to get their pinchers on human technology!

This was a really good story. Barlennan and his friends have lots of exciting adventures and, with the advice of the humans communicating with them from the moon base, manage to reach the disabled rocket and conclude their mission, helping not only the research scientists but gaining a lot for their own people. Just a fun read, with a lot of hard science for the science buffs to enjoy.