Most people have seen a weather balloon. Weather balloons provide an important weapon in the armoury of modern science for measuring the atmosphere to make weather forecasts. In fact balloon-carried scientific measuring instruments have a very long history, extending back to the origins of manned flight in the eighteenth century. Many fundamental findings have been made using scientific balloons, as they conveyed early investigators or their instruments to frontiers of the unexplored. Amongst other discoveries such as the layering of the atmosphere, scientific balloons directly facilitated the discovery of high energy particles originating outside our solar system - cosmic rays. They are able to provide information on what makes up the atmosphere as well as revealing where the different parts of the atmosphere are. Hundreds of weather balloons are launched every day around the world. However, much as they are well-equipped for their short and harsh operating life with batteries, a radio transmitter and weather sensors, they are rarely used for anything more than weather measurements. Some are used to measure the thinness of the ozone layer, and some have been used to probe the electrical structure of thunderstorms, but globally they are under-used as a scientific resource. For little extra cost and no additional receiving equipment, existing daily weather balloon flights can provide a new network of scientific measurements. This could include the atmosphere's chemical composition, finding where turbulence affects aircraft safety and discovering if cloud droplets are forming. To harness this under-utilized scientific resource requires new compact and inexpensive sensors for the measurements, and a method to integrate the sensors with the weather balloons. Most sensors are electronic, and provide voltages representing the quantities they measure. These voltages can be converted to information for transmission over the weather balloon's radio system. The modern weather balloon systems used in the UK do include spare capacity for such extra signals, but this is hardly ever used other than for occasional ozone measurements. By using simple interface circuitry including a miniature computer, the extra measuring capability can be made available for the additional sensors' measurements to be delivered to the receiving station computer. Fortunately, beyond the actual sensors required and the interface circuitry on the weather balloon, nothing more than software is needed to retrieve these extra measurements using the standard equipment already at weather balloon sites. Compared with the cost of flying aircraft therefore, enhancing the weather balloon network generates a relatively cheap method of obtaining widespread atmospheric chemistry and physics measurements. Another helpful aspect is that weather balloons do not suffer from the complications of flight plans and aircraft regulations which restrict even robotic aircraft. Weather balloon launch permissions are readily obtained, allowing measurements at short notice in response to changing conditions. This project will, firstly, design and make a disposable interface system to connect the new science sensors to the weather balloon. As many possible sensors are now available, it will be flexible and programmable. Because weather balloons are almost always ultimately lost, both sensors and interface system need to be cheap. This is possible because of the wide range of electronic devices now available. Secondly, the project will experiment with sensors to measure solar radiation, cloud droplets, the charge on cloud droplets and local turbulent motion, tested against surface measurements and by using flights near weather radars. These sensors have been chosen first as they will provide information on clouds, which, as well as giving us weather, are a key element of the climate system which has to be better understood.